New Geochemical and Geochronological Constraints on the Genesis of the Imourkhssen Cu±Mo±Au±Ag Porphyry Deposit (Ouzellagh-Siroua Salient, Anti-Atlas, Morocco): Geodynamic and Metallogenic Implications

Abstract

The Imourkhssen porphyry Cu±Mo±Au±Ag deposit is located at the Ouzellagh-Siroua Salient (OSS) straddling the boundary between the central Anti-Atlas and the central High Atlas. It is characterized by a typical porphyry-style mineralization. The volcanic rocks are intruded by numerous magmatic rocks of the Ouarzazate Group (580–539 Ma), referred to as the Late Ediacaran magmatic suites (LEMS). Of these, the Askaoun, Imourkhssen, and Imourgane granites are the most significant as they are related to the porphyry mineralization. The entire set is intruded by the Zaghar mafic dyke swarms. Zircon U-Pb dating of the Imourkhssen granite and the ore-bearing granite porphyry shows that these intrusive rocks were emplaced at 558 ± 1 and 550 ± 2 Ma, respectively. Moreover, the whole-rock major and trace element geochemistry reveal a high-K calc-alkaline I-type composition, consistent with an emplacement in a post-collisional setting under a trans-tensional tectonic regime. Ore bodies are hosted by the Askaoun granodiorite as well as the Imourgane granite. The mineralization occurs as fine-grained dissemination and infills of hydrothermally altered NNE–SSW to N–S trending veins and veinlets. Ore-related hydrothermal alteration consists of potassic, chlorite-sericite, serecitic, and propylitic mineral assemblages along with pervasive silicification and pyritization, providing a porphyry-style alteration pattern. The ore periods comprise supergene and magmatic-hydrothermal periods. The latter includes primary dissemination and secondary NNE–SSW to N–S ore-bearing system stages. The occurrence of molybdenite is either restricted to the potassic and chlorite-sericite alteration zones of the ore-bearing granite as fine disseminations or alternatively as veinlet infills within the propylitic halos. The molybdenite occurrences along with pyrite, chalcopyrite, galena, and tennantite dissemination are assigned to the primary ore stage, while the NNE–SSW to N–S ore-bearing system is related to the secondary ore stage. It consists of pyrite, chalcopyrite, bornite, covellite, diagenite, sphalerite, hematite, galena, gold, and chenguodaite. The predominance of cockade and crack-and-seal textures suggest multiple episodes of ore-forming fluid circulations under epithermal conditions. The supergene stage is achieved by subordinate malachite, azurite, barite, hematite, epsomite, and chrysocolla. From the descriptions above, we argue that the Imourkhssen Cu±Mo±Au±Ag mineralization shares many mineralogical and paragenetic attributes of porphyry-copper deposits.

1. Introduction

Porphyry deposits are a critical type of magmatic-hydrothermal ore deposit, known for their large tonnage and significant contribution to the production of copper, gold, and molybdenum, encouraging current research and exploration [1,2]. These deposit types are widely documented, but their origin and evolution are in many cases still poorly constrained due to: (i) the diversity of their geodynamic settings, (ii) the variability of the host rocks, and (iii) the zoning in both paragenetic succession and alteration assemblage [1,3]. Indeed, porphyry copper deposits are commonly associated with medium to high potassic calc-alkaline (shoshonitic) or alkaline I-type magnetite series [4]. This type of magmatism is frequently associated with subduction zones in continental arc settings [5], as well as with orogenic collapse zones linked to post-collisional events [6].

Porphyry copper deposits range in age from Archean to Holocene, although the most productive are Jurassic or younger [3]. A large number of these deposits occur along the peri-pacific belt (Figure 1), particularly in the Andean (Chili, Peru) and North American Cordillera (Colorado belt), where the three largest molybdenum porphyry deposits occur (e.g., Climax, Urad-Henderson, and Emmons Mounts [7]).

Porphyry ore deposits display a distinctive, broad-scale alteration-mineralization zoning pattern that includes from the core to the periphery, sodic-calcic, potassic, chlorite-sericite, serecitic, advanced argillic, and propylitic mineral assemblages [1,7]. Potassic alteration is usually the innermost alteration, which grades irregularly into propylitic alteration patterns [9]. The chlorite-sericite zone is considered as the early stage of the phyllic alteration overprinting the previous potassic mineral assemblage [9]. Phyllic (or serecitic) alteration is observed in the field as bleached outcrops [10]. It is a pyrite-dominated shell and also contains quartz and sericite minerals [1]. The extreme, distal, and shallowest part of the alteration zone is the propylitic alteration, which consists of chlorite, carbonate, epidote, adularia, and albite [1,11]. These widespread and distinctive hydrothermal zones provide a useful footprint for porphyry copper exploration [4].

In the Anti-Atlas belt of Morocco, many examples of deposits seem to exhibit some of the characteristics that are indicative of porphyry copper systems, such as Tiouit [12,13], the “Patte d’Oie” part of Bouskour [6,14], and Ismlal Au stockwork deposits [15]. Here, we describe the geological features of the Imourkhssen deposit, which is thought to be the first example of a Neoproterozoic porphyry Cu±Mo±Au deposit in Morocco [16]. This study provides new geological, geochemical, geochronological, and ore features on the Imourkhssen Cu±Mo±Au±Ag porphyry deposit. The timing of the ore emplacement is discussed in the framework of a multi-pulse featuring Ouarzazate Silicic Large Igneous Province (SLIP) during the concluding stages of the Pan-African orogeny, within the context of an extensional regime along the northern metacratonic border of the West African craton (WAC).

2. Regional Geology

2.1. The Anti-Atlas

The Anti-Atlas Mountains of Morocco are a WSW–ENE oriented belt formed by the Precambrian basement unconformably overlain by slightly folded Paleozoic sedimentary formations (Figure 2B). The orogen records the effects of two main periods of tectono-magmatic activities linked to the Paleoproterozoic Eburnean (2.07–2.20 Ga) and Neoproterozoic Pan-African (885–539 Ma) orogenies [17,18].

The Eburnean terranes form the crystalline basement into which some Neoproterozoic Pan-African successions were deposited and subsequently deformed in four stages, which likely correspond to a Wilson cycle: (1) Rifting and break-up (>800 Ma) of an unknown continent to which belonged the WAC coincident with rift-related magmatism activity [20]. (2) Formation of island arcs at 770–720 Ma [21]. (3) Ocean closure (720–630 Ma), highlighted by a polyphase accretion of oceanic rocks, as a diverse amphibolite to greenschist facies metamorphosed assemblage of ophiolitic complexes [22,23,24,25]. (4) Post-collisional period (630–539 Ma), which evolved from a transpressive to a transtensive tectonic setting, with the emplacement of huge high potassic calc-alkaline to shoshonitic volcano-plutonic rocks, accompanied by sedimentary successions deposited into pull-apart basins [17,26,27]. This final stage consists of the deposition of:

(i)

The Saghro Group (620–600 Ma), which consists of volcanic and volcano-sedimentary rocks of andesite-basaltic and andesitic to trachytic compositions, with rare sedimentary intercalations [19,25].

(ii)

The Bou Salda Group successions (600–580 Ma), which are characterized by poorly sorted sediments and abundant high-K calc-alkaline volcanic and intrusive rocks [20,28].

(iii)

The Ouarzazate Group (580–539 Ma), which is composed mainly of high potassic calc-alkaline volcanic, volcanoclastic and plutonic rocks [27,29,30]. This Late Neoproterozoic magmatism is also widespread in the High Atlas and Meseta [18,30].

In the Anti-Atlas, Late Ediacaran magmatic activity coupled with strong extensional trans-tensional tectonic structures are invoked to explain the pervasive hydrothermal activity at the origin of the genesis of some of the world-class precious metal, base metal, and SEDEX-type deposits that have been documented through the central and eastern parts of the Anti-Atlas [15,27,28] and have recently been defined as the Saghro domain (Figure 2B,C) [30].

2.2. Deposit-Scale Geology

The Cu±Mo±Au±Ag Imourkhssen deposit is hosted by granitic intrusions (Figure 3) stratigraphically assigned to the Ouarzazate (580–539 Ma) Group and belongs to the Ouzellagh-Siroua Salient (OSS) [31]. These intrusions intrude the rocks of the Saghro Group (630–610 Ma; [26]) and comprise a wide spectrum of igneous rocks spanning from volcanic to plutonic bodies. These rocks belong to the Late Ediacaran magmatic suites (LEMS), comprising the Assarag, Amassine, and Ougougane suites.

Figure 3. Geological map of the studied area. Modified from [21,29,32].

Figure 3. Geological map of the studied area. Modified from [21,29,32].

In the Imourkhssen area, the Assarag suite includes the large Askaoun batholith, which consists of the Askaoun granodiorite and quartz diorite. This batholith covers 800 km² in the NW part of the OSS [21]. The Amassine suite is represented by the star-shaped Imourkhssen granite. This suite was previously interpreted to encompass an ore-bearing granite porphyry. In this study, the latter lithotype is referred to as “the Imourgane granite” since it is actually related the Ougougane suite (see geochronology section). This porphyritic intrusion consists of a succession of rhyolite, microgranite, and granite, all of which are crosscut by the Zaghar mafic dyke swarms (Figure 4).

The emplacement of the LEMS is related to the development of many base and precious metal deposits in the OSS, including the Ag-Hg Zgounder ore deposit [33] and the Cu-Co-Mo Inki mineralization [21]. Nonetheless, the Imourkhssen deposit has been identified as a Cu±Mo±Au porphyry mineralization associated with Imourkhssen and Askaoun granitoids [16].

This study focuses on the ore feature of the Cu±Mo±Au±Ag Imourkhssen ore deposit and discusses the emplacement of the LEMS in the framework of a long-lived Ouarzazate Silicic large igneous province (see discussion section).

Figure 4. The Zaghar dykes crosscut the Ougougane granite.

Figure 4. The Zaghar dykes crosscut the Ougougane granite.

3. Sampling and Analytical Methods

Sampling was carried out on both fresh and altered rocks from the Imourkhssen area, including the abandoned Talat nl’bour galleries. More than seventy samples were collected. The representative samples were selected for petrographic, mineralogical, geochemical, and geochronological studies (Appendix A,

Table A1. Characteristics and localization of the samples used for different studies.

ID sample	Suite	Rock	Analysis	Location	Characteristics
23IM27	Assarag	Askaoun granodiorite	Petrography Geochemistry	N 30°55,13′/W 007°52,05′	The sample is collected near the Talat nl’bour galleries
J23IM13	Amassine	Imourkhssen granite	Petrography Geochronology	N 30° 56,72′/W007° 51,57′	Fresh sample collected from the star-shaped intrusion
23IM13	Ougougane	Imourgane granite	Petrography Geochemistry	N30° 55,36′/W007° 52,28′	The sample exhibits molybdenite dissemination
J23IM09	Ougougane	Imourgane granite	Geochronology	N30° 55,91′/W007° 51,71′	The sample exhibits a molybdenite vein
23IM20		Zaghar dyke	Petrography Metallogeny	N30° 57,65′/W007° 52,22′	The dyke (50 cm thick) cut across the Imourgane granite. This dyke exhibit sulfide dissemination (Figure 15D)
23IM07A	Ougougane	Ougougane microgranite dyke	Geochemistry	N30° 56,04′/W007° 51,70′	The dyke (30 cm thick) cut across the quartz-diorite
23IM09	Ougougane	Ougougane microgranite dyke	Geochemistry	N30° 56,02′/W007° 51,80′	N175-oriented dyke, with a thickness of about 50 cm
23IM19	Ougougane	Imourgane	Geochemistry	N30° 57,70′/W007° 52,51′	Fresh sample
23IM22	Ougougane	Ougougane rhyolite	Geochemistry	N30° 53,80′/W007° 53,03′	The sample is cut by a N130 Qz-Hm vein
23IM24	Ougougane	Ougougane microgranite dyke	Geochemistry	N30° 52,51′/W007° 53,62′	This dyke is cut by a Zaghar mafic dyke
23IM26B	Ougougane	Imourgane	Geochemistry	N30° 55,35′/W007° 52,20′	Fresh sample
23IM26C	Ougougane	Imourgane	Geochemistry	N30° 55,38′/W007° 52,11′	The intrusion is cut by a N70 hematite lens
23IM26D	Ougougane	Imourgane	Geochemistry	N30° 55,52′/W007° 51,98′	Fresh sample near molybdenite veinlets
23IM17A	Assarag	Askaoun granodiorite	Geochemistry	N30° 56,15′/W007° 51,57′	This sample is near sulfide dissemination
23IM23	Assarag	Askaoun granodiorite	Geochemistry	N30° 53,81′/W007° 53,05′	Fresh sample
23IM25	Assarag	Askaoun granodiorite	Geochemistry	N30° 53,95′/W007° 53,23′	The intrusion is cut by the N130 doleritic dyke
23IM26A	Assarag	Askaoun granodiorite	Geochemistry	N30° 52,27′/W007° 52,00′	The sample is collected near the Talat nl’bour galleries
23IM27	Assarag	Askaoun granodiorite	Geochemistry Metallogeny	N30° 55,13′/W007° 52,05′	The sample displays sulfide disseminations
23IM07B	Assarag	Askaoun quartz-diorite	Geochemistry	N30° 56,03′/W007° 51,71′	Fresh sample
23IM14A	Assarag	Askaoun quartz-diorite	Geochemistry	N30° 55,34′/W007° 52,39′	The intrusion is cut by the Ougougane dyke
23IM28	Assarag	Askaoun quartz-diorite	Geochemistry	N30° 55,57′/W007° 51,92′	Fresh sample
22IM05	Ougougane	Imourgane	X-Ray Diffraction	N30° 55,57′/W007° 51,92′	Altered sample collected from serecitic alteration zone
22IM02	Ougougane	Imourgane	X-Ray Diffraction	N30° 55,22′/W007° 52,05′	Fresh sample from the Imourgane granite
22IM17	Assarag	Askaoun granodiorite	X-Ray Diffraction Metallogeny	N30°54,97′/W007°51,97′	The sample is collected from a quartz-chlorite sulfide vein cutting across the granodiorite. Sulfides are shown in Figure 15E
23IM13C	Assarag	Askaoun granodiorite	X-Ray Diffraction	N30°54,99′/W007°51,96′	The sample is collected from a quartz-chlorite sulfide vein cutting across the granodiorite
22IM20	Ougougane	Imourgane	X-Ray Diffraction	N30°55,32′/W007°51,93′	The sample is collected from a silicic alteration zone
T1	Ougougane	Imourgane	X-Ray Diffraction	N30°55,21′/W007°52,20′	The sample is collected from the wall’s galleries
J23IM08	Assarag	Askaoun granodiorite	Metallogeny	N30°55,57′/W007°51,80′	Sulfide dissemination (Figure 15C)
J23IM10	Ougougane	Imourgane	Metallogeny	N30°55,91′/W007°51,71′	Sulfide dissemination (Figure 15F)

).

Polished thin sections representing different alteration assemblages and mineralized veins were examined using plane-polarized and reflected-light microscopy. For phase identification, and for the local quantitative mineralogical and elementary compositions, more than nine thin sections were analyzed at the research center of the Faculty of Sciences of Agadir, Ibn Zohr University using a JEOL JSM IT-100 scanning electron microscope. The resolution was at most 100 nm, where both backscattered electron and energy-dispersive spectroscopy were used.

Six samples were also analyzed for mineral composition using a D8 ADVANCE Twin X-ray diffractometer (XRD). The diffractometer has a two-theta geometry with a copper sealed tube x-ray source, producing Cu Kα1 radiation at a wavelength of 1.5406 Å. The x-rays are issued from a generator operating at 40 kV and 25 mA and its operating energy is 100 W. XRD data were collected from 5 to 100° ± 0.05 θ. The diffraction patterns obtained were used for mineral identification and semi-quantitative assessment of mineral content, indexed using X’Pert HighScore Plus v. 3. software.

For whole-rock geochemistry, the major and trace elements of seventeen samples were analyzed by ICP–OES/ICP–MS (fusion of inductively-coupled plasma–optical emission spectrometry and inductively-coupled plasma–mass spectrometry) methods at Actlabs laboratory, Canada (Appendix A,

Table A2. Whole-rock major and trace element geochemical data of the Late Ediacaran granite of the TV area (in percent “%” for major elements and part-per-million “ppm” for trace elements).

	23IM7A	23IM09	23IM19	23IM22	23IM24	23IM7B	23IM14	23IM28	23IM13	23IM26	23IM26’	23IM26”	23IM17	23IM23	23IM25	23IM26”’	23IM27
SiO2	72.39	76.68	73.72	77.02	75.54	57.4	64.75	58.91	73.25	74.53	76.49	75.99	66.54	64.64	64.31	66.99	61.83
Al2O3	14.11	11.98	13.21	12.27	12.26	17.43	15.55	16.57	13.1	13.16	13.24	12.95	14.47	14.17	15.52	14.96	14.88
FeO	0.54	0.4	1.93	0.76	0.95	9.01	5.49	7.76	1.9	2.29	0.66	1.66	4.1	5.57	5.25	4.57	5.49
MnO	0.009	0.013	0.034	0.007	0.024	0.115	0.08	0.132	0.019	0.063	0.007	0.032	0.074	0.107	0.091	0.085	0.135
MgO	0.12	0.12	0.29	0.36	0.38	4.46	1.9	2.76	0.62	0.62	0.24	0.42	1.64	2.34	2.21	1.77	2.74
CaO	0.14	0.23	0.96	0.14	0.12	0.64	2.29	4.81	0.23	0.2	0.15	0.48	1.15	2.22	3.43	3.18	3.77
Na2O	3.35	2.93	3.78	3.52	3.47	2.31	2.21	3.09	3.68	3.79	3.26	3.66	3.9	3.4	3.49	3.41	4.18
K2O	6.87	5.72	3.9	4.05	5	2.9	4.11	1.77	4.44	3.88	4.81	4.32	4.04	4.08	3.58	3.66	2.9
TiO2	0.067	0.083	0.179	0.049	0.043	0.712	0.71	0.778	0.191	0.181	0.203	0.179	0.527	0.721	0.697	0.615	0.71
P2O5	0.02	0.04	0.06	0.02	0.02	0.1	0.14	0.15	0.06	0.05	0.05	0.06	0.1	0.13	0.14	0.12	0.15
LOI	0.26	0.64	0.79	0.89	3.15	4.15	1.86	2.52	1.1	0.3	0.71	1.02	1.58	1.58	0.9	0.8	2.07
Total	97.86	98.84	98.85	99.07	101	99.22	99.09	99.25	98.59	99.06	99.83	100.8	97.97	98.95	99.62	100.2	98.84
Sc	1	2	3	2	2	14	13	16	3	2	3	2	9	14	13	11	14
Be	1	1	2	1	<1	2	2	1	1	2	2	2	2	1	1	1	1
V	<5	<5	9	<5	<5	108	69	135	7	8	9	9	65	105	96	77	78
Ba	1812	1313	815	674	971	376	1946	437	674	645	500	771	844	1068	1055	1006	797
Sr	62	78	123	53	47	93	231	376	54	56	34	87	187	220	342	256	386
Y	11	14	24	12	10	18	27	18	23	20	23	17	22	25	22	22	21
Zr	75	71	136	58	52	144	261	142	147	145	141	126	274	246	242	254	258
Cr	<20	<20	<20	<20	<20	40	30	30	<20	<20	20	<20	<20	30	30	30	30
Co	76	80	63	72	84	34	59	42	129	54	56	68	53	77	69	65	52
Ni	<20	<20	<20	<20	<20	30	<20	30	<20	<20	<20	<20	<20	<20	<20	<20	<20
Cu	<10	10	<10	<10	30	40	10	70	<10	<10	<10	<10	20	50	40	50	140
Zn	<30	60	<30	<30	<30	90	70	110	<30	<30	<30	<30	120	90	70	70	110
Ga	15	12	17	14	15	25	20	23	17	17	17	17	19	18	19	19	20
Ge	1	1	2	<1	<1	1	1	1	1	1	1	1	1	1	1	1	1
As	<5	<5	<5	<5	<5	<5	5	17	<5	<5	<5	<5	9	8	10	15	9
Rb	153	141	140	104	133	154	140	63	129	95	137	147	126	147	116	144	105
Nb	3	7	9	6	6	8	10	7	11	12	11	10	9	9	9	9	9
Mo	<2	<2	<2	<2	<2	<2	<2	<2	> 100	18	5	63	3	<2	2	<2	<2
Ag	<0.5	<0.5	<0.5	<0.5	<0.5	<0.5	<0.5	<0.5	<0.5	<0.5	<0.5	<0.5	0.5	<0.5	<0.5	<0.5	<0.5
La	24.3	28.2	30.3	11.6	8.4	22.9	35.8	22.7	60.6	47.3	13.1	45.5	23.9	29.7	29.1	32.4	30.3
Ce	61.9	49.9	58.3	23.1	17.7	38.8	72.7	43.7	126	101	26.6	86.9	54.1	60.8	58.8	63.4	61.4
Pr	4.79	5.62	6.66	2.51	2.08	4.76	8.49	5.25	14.1	10.1	3.11	9.28	5.83	7.14	6.79	7.11	6.85
Nd	15.9	18.9	23.4	8.6	7.3	17.7	31.6	20.8	48.2	33.5	11.4	31.9	22.2	26.2	25.2	26.3	26
Sm	2.5	3.2	4.1	1.7	1.6	3.4	6.2	4.2	7.5	5.3	2.5	4.8	4.8	5.1	4.8	5	5
Eu	0.41	0.5	0.56	0.21	0.22	0.69	1.08	1.1	0.6	0.7	0.37	0.57	0.83	0.85	0.91	0.84	0.96
Gd	1.8	2.5	3.7	1.5	1.5	3.2	5.4	3.6	4.9	3.7	2.7	3.2	4.3	4.6	4	4.1	4.2
Yb	1.4	1.8	2.9	1.4	1.5	2.2	2.8	1.9	2.7	2.5	2.6	2	2.5	2.3	2.1	2.2	2.3
Lu	0.25	0.31	0.47	0.25	0.25	0.36	0.43	0.29	0.43	0.43	0.41	0.34	0.38	0.39	0.35	0.37	0.35
Hf	2.7	2.7	4.2	2.1	2	4.3	7.4	3.9	4.2	4.5	4.2	3.7	7.5	6.6	6.5	7.2	7
Ta	1.8	2.3	2.2	1.9	2	0.9	1.6	1	2.9	1.9	2.2	2.1	1.5	1.6	1.5	1.4	1.4
Tb	0.3	0.4	0.6	0.3	0.3	0.5	0.8	0.6	0.7	0.6	0.5	0.5	0.7	0.7	0.6	0.6	0.7
Dy	1.7	2.3	3.9	1.8	1.8	3.5	4.9	3.3	3.9	3.5	3.5	2.9	4.1	4.2	3.8	4.2	4
Ho	0.3	0.5	0.8	0.4	0.4	0.7	1	0.6	0.8	0.7	0.7	0.6	0.9	0.8	0.7	0.8	0.8
Er	1.1	1.5	2.4	1.2	1.2	2.1	2.8	1.9	2.3	2.3	2.4	1.8	2.4	2.5	2.2	2.4	2.3
Tm	0.19	0.25	0.38	0.21	0.2	0.31	0.42	0.27	0.37	0.35	0.37	0.29	0.36	0.37	0.32	0.33	0.34
W	616	666	548	561	620	151	457	249	1020	455	540	670	393	536	479	429	402
Tl	0.6	0.7	0.4	0.4	0.6	0.5	0.4	0.2	0.5	0.4	0.4	0.5	0.5	0.6	0.4	0.6	0.4
Bi	<0.4	<0.4	<0.4	<0.4	<0.4	<0.4	<0.4	<0.4	<0.4	<0.4	<0.4	<0.4	<0.4	<0.4	<0.4	<0.4	<0.4
Th	18.8	18.4	19.7	8.7	8.8	8.1	16.1	6.6	15.8	15.9	17	15.9	23.1	15	15.2	18	13.2
U	4.2	5.2	6.5	4.2	5.1	3.4	8.5	4.2	4.5	8.5	12	8	14.3	4.6	8.4	5.8	8.3
In	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2	<0.2
Sn	<1	<1	<1	<1	1	1	1	1	2	5	2	1	2	1	1	1	1
Sb	<0.5	<0.5	<0.5	<0.5	<0.5	0.9	1.3	2	<0.5	<0.5	<0.5	<0.5	1.7	2.1	2	3.5	3.5
Cs	0.9	0.7	0.7	0.9	0.5	2.2	2.3	0.9	1.2	1	1.2	0.8	0.8	1.8	0.9	1	0.7
Pb	<5	14	9	<5	6	<5	20	7	<5	7	<5	7	25	24	14	24	18

).

Moreover, two powdered molybdenite samples from Imourgane granite were analyzed at the Robert M. MacKay electron microprobe laboratory, located in the Department of Earth Sciences, Dalhousie University, Halifax. The analyses were carried out with a JXA-8200 electron microprobe, using the internal standards for quality control (Appendix A,

Table A3. Quantitative results for the molybdenite dissemination (MD) and the molybdenite veinlet (MV) samples.

Element Line	Net Counts	Weight %	Weight % Error	Atom %	Atom % Error	Compnd %
MD sample
Si K	1550	0.32	± 0.06	0.60	± 0.11	0.32
Si L	0	---	---	---	---	---
S K	168319	41.59	± 1.59	67.77	± 2.59	41.59
S L	0	---	---	---	---	---
Mo L	177420	58.09	± 2.30	31.63	± 1.25	58.09
Mo M	1229	---	---	---	---	---
Total		100.00		100.00		100.00
MV sample
Mg K	827	0.16	± 0.02	0.33	± 0.05	0.16
Al K	439	0.08	± 0.03	0.16	± 0.05	0.08
Si K	3130	0.59	± 0.05	1.07	± 0.10	0.59
Si L	0	---	---	---	---	---
S K	194626	43.51	± 0.65	68.85	± 1.03	43.51
S L	0	---	---	---	---	---
Fe K	418	0.45	± 0.11	0.41	± 0.10	0.45
Fe L	0	---	---	---	---	---
Mo L	186335	55.21	± 1.13	29.19	± 0.60	55.21
Mo M	1586	---	---	---	---	---
Total		100.00		100.00		100.00

).

For geochronological purposes, two granite samples were dated by LA–ICP–MS U-Pb on zircon at the Geotop Research Center, University of Quebec in Montreal (UQAM). Each sample was crushed and sieved to obtain a uniform grain size fraction of 50–250 μm. The resulting fraction was then introduced over a Wilfley table to separate the smaller and denser minerals. The fine dense fraction was collected and then processed with heavy liquids (methylene diodide) and a Franz isodynamic separator using a current up to 1 ampere to concentrate zircon grains.

Hundreds of clear, well-formed zircon grains were hand-picked from each sample under a binocular microscope, avoiding inclusions and fractures. Selected grains were then mannealed in a muffle furnace at 1000 degrees for 48 hours before being mounted in epoxy resin on a standard 1-inch round mount, polished, and imaged on a Hitachi S-3400 Variable Pressure SEM at an accelerating voltage of 20 kV using a Centaurus Cathodoluminescence (CL) detector to outline the growth zoning, rims, and inherited cores within individual grains and guide the spot selection for in situ laser ablation analysis. The U-Pb analysis was performed using a Nu Atom single collector mass spectrometer coupled with a photon machine G2 193 nm excimer laser, following a modified procedure reported in [34], adding 3 ml/min N2 before the torch to reduce oxide formation in the plasma. The sensitivity of the mass spectrometer was optimized using U from a NIST610 glass, and the gas flow was adjusted by to ensure a U/Th of 1 and Th/ThO of 1 × 10⁻³ for the NIST glass. We used a laser energy of 4.54 J/cm², a repetition rate of 6 Hz, and a 30 μm ablation spot. Measurements were conducted using a sample reference material bracketing approach, with sets of 15 unknown samples bracketed by two primary reference samples and at least one secondary reference grain analysis for quality control purposes.

The 91500 (1065 Ma, [35]) and Plešovice [36] were used respectively as primary and secondary reference materials. The two samples were analyzed over one analytical session. The individual analyses were processed and corrected for down-hole fractionation using Iolite v4 software with the U-Pb geochronology data reduction scheme (DRS) [35]. Analyses with detectable ²⁰⁴Pb were excluded prior to data reduction, and no general Pb correction was applied. The repeated analyses of Plešovice produced a weighted mean ²⁰⁶Pb/²³⁸U age of 337 ± 1 Ma, in agreement within error with its known age ([36]; see Appendix A,

Table A4. LA–ICP–MS U-Pb data for the J23IM09 and J23IM13 samples of the Imourgane and Imourkhssen granites, respectively.

							Data for Tera–Wasserburg Plot						Data for Wetherill Plot					Dates						Conc -Age	2s	% Conc
Sample	f206c	206Pb	Uppm	Th/U	206Pb/204Pb	1s%	238U/206Pb	1s%	207Pb/206Pb	1s%	208Pb/206Pb	1s%	207Pb/235U	1s%	206Pb/238U	1s%	Rho	207Pb/235U	2s	206Pb/238U	2s	207Pb/206Pb	2s
J23IM09
IM09_42	1.82	113,465.01	1856	0.22	1628.79	32.76	22.04	2.0	0.06581	2.26	0.101656532	1.542769	0.4116	2.8	0.04538	2.1	0.60	350.0	16.4	286.1	11.8	799.4	94.6	291.6	12.0	36.3
IM09_13	2.06	161,550.20	2640	0.22	994.70	36.67	20.04	1.2	0.07010	1.33	0.118650273	1.143269	0.4821	1.5	0.04990	1.1	0.51	399.5	10.2	313.9	6.9	930.5	56.1	322.6	7.0	34.0
IM09_50	0.78	130,894.92	1530	0.60	−10,479.33	−55.20	17.08	1.7	0.06632	1.44	0.114750055	1.084423	0.5352	2.6	0.05856	1.8	0.85	435.3	18.2	366.9	12.6	815.6	59.5	336.3	12.1	45.9
IM09_8	−0.47	136,017.00	1340	0.20	2367.08	44.04	13.80	1.9	0.05827	1.18	0.068617945	2.542060	0.5821	2.5	0.07249	2.1	0.86	465.8	18.3	451.1	18.7	539.0	55.0	459.2	18.3	86.6
IM09_30	−0.04	162,532.62	1901	0.22	−302.55	−203.07	12.22	0.8	0.05836	0.90	0.055314891	1.154858	0.6581	1.0	0.08182	0.8	0.53	513.5	8.2	507.0	7.5	542.5	39.3	509.6	6.9	95.7
IM09_28	−0.09	115,708.43	1276	0.28	3101.82	41.18	12.00	2.6	0.06029	2.27	0.063703567	1.698743	0.6923	4.2	0.08333	2.7	0.88	534.2	34.8	515.9	27.1	613.0	96.4	509.3	26.8	89.0
IM09_29	−0.28	148,949.72	1918	0.43	231.34	599.99	11.81	1.6	0.05738	1.77	0.106412593	2.185354	0.6695	2.1	0.08466	1.6	0.55	520.4	17.1	523.9	16.5	505.2	80.2	522.3	14.8	107.4
IM09_36	0.09	165,969.27	1000	0.31	1162.37	100.19	11.74	1.6	0.05969	1.20	0.080819076	1.358081	0.7007	1.5	0.08518	1.5	0.71	539.2	12.9	527.0	15.4	591.3	50.4	536.6	12.8	91.0
IM09_38	−0.10	97,428.57	583	0.28	185.45	204.35	11.67	0.5	0.05898	1.32	0.078596684	2.589182	0.6964	1.3	0.08568	0.5	0.18	536.7	10.9	529.9	5.2	565.4	57.4	530.8	5.0	98.2
IM09_47	0.28	99,263.60	937	0.33	−2107.03	−29.71	11.66	0.6	0.05814	1.34	0.083235690	1.769080	0.6874	1.3	0.08579	0.6	0.20	531.2	11.0	530.6	5.9	534.1	58.6	530.7	5.6	102.3
IM09_18	0.71	128,793.30	1105	0.23	−17.07	−6060.72	11.64	0.7	0.05913	2.02	0.067701160	2.391053	0.6998	2.0	0.08588	0.7	0.22	538.7	17.1	531.1	7.3	570.8	87.6	531.8	7.2	93.2
IM09_33	−0.05	126,750.48	688	0.30	4346.80	34.68	11.64	0.5	0.05920	0.96	0.076141230	1.083022	0.7009	1.0	0.08590	0.5	0.34	539.3	8.5	531.2	4.7	573.6	42.0	532.2	4.6	95.8
IM09_15	−0.32	137,915.60	1182	0.26	583.68	93.37	11.59	0.8	0.06018	1.59	0.064202238	1.395470	0.7157	1.6	0.08629	0.8	0.25	548.1	13.5	533.5	8.2	609.3	68.9	536.5	7.7	89.3
IM09_27	0.35	177,923.11	1987	0.21	4040.33	32.73	11.54	0.9	0.05922	0.91	0.056072724	0.776586	0.7069	1.2	0.08662	0.9	0.67	542.9	10.4	535.5	9.3	574.0	40.0	537.9	9.0	95.4
IM09_49	0.29	115,149.47	956	0.34	−1373.76	−98.54	11.54	2.1	0.05892	1.84	0.092323916	2.197912	0.7038	2.4	0.08667	2.0	0.65	541.1	20.4	535.8	20.5	563.3	82.8	538.4	18.6	97.7
IM09_24	−0.54	68,982.24	628	0.42	−5165.33	−322.65	11.52	0.6	0.05965	1.37	0.102088125	1.580077	0.7135	1.3	0.08680	0.6	0.14	546.8	11.1	536.6	5.9	589.8	58.9	538.4	5.5	94.4
IM09_37	0.15	145,672.41	814	0.30	788.66	88.77	11.42	0.8	0.05946	0.96	0.077821272	1.931281	0.7174	1.0	0.08754	0.8	0.43	549.1	8.5	541.0	8.0	582.9	42.0	544.6	7.0	95.4
IM09_41	−0.05	147,896.77	1350	0.36	273.42	198.16	11.40	0.8	0.05835	0.89	0.091891479	1.362570	0.7058	1.1	0.08776	0.9	0.64	542.2	9.4	542.3	8.9	542.1	38.3	542.2	8.3	102.5
IM09_9	−0.01	99,319.66	725	0.27	1085.33	49.34	11.32	0.5	0.05841	1.18	0.068986597	1.371982	0.7113	1.2	0.08836	0.5	0.14	545.5	9.7	545.8	4.9	544.4	51.6	545.8	4.6	102.9
IM09_23	−0.55	100,882.77	851	0.45	−3659.90	−38.32	11.28	0.5	0.05854	1.18	0.120289034	3.089733	0.7155	1.2	0.08868	0.5	0.26	548.0	10.4	547.7	4.9	549.1	52.2	547.8	4.8	103.6
IM09_12	0.61	37,544.25	358	0.23	−81.17	−154.45	11.23	0.7	0.05857	1.93	0.059050253	1.809297	0.7188	1.9	0.08904	0.7	0.22	549.9	16.5	549.9	7.9	550.2	83.7	549.9	7.6	107.7
IM09_22	−0.28	128,486.91	1012	0.27	−5413.91	−26.57	11.21	0.6	0.05893	1.03	0.068883865	2.037317	0.7246	1.0	0.08923	0.6	0.30	553.4	8.9	551.0	6.3	563.4	45.2	551.6	5.8	100.0
IM09_31	0.31	153,624.47	904	0.26	−13,357.62	−30.23	11.20	0.6	0.05922	1.00	0.065719123	1.417447	0.7289	1.1	0.08930	0.7	0.51	555.9	9.8	551.4	7.2	574.3	43.0	552.3	7.0	99.4
IM09_21	0.19	105,753.52	790	0.36	−3438.12	−28.15	11.19	0.5	0.05820	1.19	0.088292712	1.228585	0.7170	1.1	0.08940	0.5	0.02	548.9	9.2	552.0	5.6	536.3	52.3	551.2	4.8	105.9
IM09_40	−0.40	116,156.81	733	0.34	−472.08	−81.88	11.18	0.5	0.05932	1.07	0.086265604	1.564234	0.7312	1.1	0.08945	0.5	0.34	557.3	9.6	552.3	5.7	577.8	46.4	553.1	5.5	98.9
IM09_19	−0.48	123,754.99	945	0.29	−530.61	−88.81	11.16	1.1	0.05791	1.14	0.072851558	1.851605	0.7153	1.5	0.08962	1.1	0.65	547.9	12.8	553.3	12.0	525.4	50.4	551.0	11.2	107.4
IM09_43	0.25	85,408.40	819	0.27	−572.00	−57.53	11.15	0.7	0.05852	1.21	0.070307712	1.586753	0.7232	1.2	0.08966	0.7	0.28	552.5	10.4	553.5	7.2	548.5	53.1	553.2	6.6	104.8
IM09_25	−0.22	117,840.94	1126	0.26	7043.18	41.79	11.15	0.4	0.05801	1.04	0.064470472	1.181541	0.7170	1.1	0.08969	0.4	0.32	548.9	9.3	553.7	4.4	529.1	45.5	553.3	4.3	108.0
IM09_32	0.45	137,655.95	753	0.24	25,790.67	30.01	11.15	0.5	0.05936	1.02	0.064902098	2.617898	0.7340	1.1	0.08972	0.5	0.37	558.9	9.4	553.9	5.4	579.4	44.7	554.5	5.3	99.0
IM09_1	0.28	76,280.36	566	0.35	−633.43	−63.69	11.10	1.4	0.06049	1.70	0.096842375	1.944924	0.7508	2.0	0.09007	1.5	0.59	568.7	17.6	555.9	15.9	620.2	71.7	560.6	15.0	92.9
IM09_17	13.53	6411.62	52	2.44	−1.72	−1273.33	11.09	1.6	0.18980	2.76	0.858867869	1.438672	2.3580	2.5	0.09014	1.6	0.16	1230.0	35.7	556.4	17.4	2739.7	90.7	579.0	17.7	20.5
IM09_7	−0.07	298,971.72	2201	0.27	13,274.24	35.64	11.10	1.0	0.05836	1.06	0.072648344	1.134184	0.7248	1.4	0.09011	1.0	0.63	553.5	11.7	556.2	11.1	542.4	47.6	555.1	10.3	104.0
IM09_20	−0.27	92,546.02	665	0.24	−71.33	−417.68	11.09	0.6	0.05787	1.42	0.061718028	1.576752	0.7189	1.4	0.09014	0.6	0.16	550.0	11.7	556.3	6.5	523.8	62.2	555.1	6.0	109.7
IM09_51	0.44	139,636.21	980	0.20	1402.05	56.65	10.97	2.1	0.05699	1.54	0.059687397	2.018009	0.7159	2.1	0.09115	2.1	0.74	548.2	18.0	562.3	22.6	490.1	67.7	549.7	17.8	116.2
IM09_5	−0.97	32,809.19	225	0.24	1992.02	928.31	10.79	0.6	0.05852	2.25	0.061926834	1.715075	0.7472	2.1	0.09265	0.6	−0.24	566.6	17.9	571.2	6.0	548.5	98.4	570.5	5.2	114.0
IM09_14	0.09	188,290.70	1901	0.34	1501.70	61.13	10.56	1.5	0.05940	2.04	0.088092270	2.132788	0.7754	2.7	0.09472	1.6	0.63	582.9	24.3	583.4	17.8	580.8	92.7	583.3	17.7	104.7
IM09_45	0.53	130,358.05	1097	0.31	−1153.73	−85.19	10.47	2.1	0.05862	1.58	0.078505954	1.819150	0.7715	2.5	0.09549	2.2	0.77	580.6	21.8	587.9	24.7	552.1	70.2	582.3	21.4	108.7
IM09_48	0.24	80,335.21	696	0.33	−1348.49	−37.90	10.47	0.7	0.05958	1.42	0.086234864	2.048943	0.7840	1.5	0.09547	0.7	0.29	587.7	13.0	587.8	7.7	587.5	61.5	587.8	7.3	103.6
IM09_16	9.41	8501.25	67	2.54	−23.84	−124.06	10.35	1.1	0.18396	2.22	0.854025101	1.320554	2.4485	2.1	0.09657	1.1	0.21	1257.0	30.9	594.3	12.2	2688.2	72.3	593.2	12.4	22.3
IM09_35	0.76	102,677.26	466	0.21	1088.03	58.95	10.25	2.1	0.05802	1.49	0.055250821	2.185268	0.7801	2.7	0.09755	2.3	0.82	585.5	23.6	600.0	25.9	529.6	66.1	588.9	23.0	118.7
IM09_2	17.04	5455.27	33	2.25	−102.27	−48.47	9.24	1.7	0.22251	3.64	0.912762464	1.977918	3.3177	2.9	0.10819	1.5	−0.07	1485.2	46.0	662.2	19.5	2998.2	110.3	722.8	18.9	22.4
IM09_34	25.20	2733.39	9	1.77	35.23	58.44	7.50	2.3	0.36833	3.54	1.054242935	2.695861	6.7716	4.7	0.13340	2.5	0.67	2082.0	83.4	807.2	37.5	3783.9	107.7	588.7	31.2	21.7
J23IM13
IM13_15	0.53	147,533.31	1119	0.40	−450.29	−98.48	12.53	1.4	0.05924	1.21	0.078222216	1.249097	0.6518	1.8	0.07984	1.4	0.72	509.6	14.6	495.1	13.6	574.8	55.5	500.4	13.2	88.2
IM13_49	0.64	110,748.18	935	0.23	−331.89	−119.70	12.00	0.7	0.06165	1.08	0.069503892	1.566091	0.7081	1.3	0.08334	0.7	0.54	543.6	10.8	516.0	7.2	661.1	46.4	518.8	7.2	81.2
IM13_34	0.80	139,589.03	1709	0.33	−4450.49	−38.85	11.75	1.0	0.05905	1.87	0.076412682	1.368866	0.6925	2.1	0.08510	1.0	0.47	534.3	17.6	526.5	9.8	567.8	81.8	526.9	9.8	96.9
IM13_35	−0.54	105,941.95	1020	0.35	−3270.66	−39.08	11.31	0.4	0.05911	1.66	0.086070256	1.822950	0.7205	1.6	0.08845	0.4	0.00	551.0	13.6	546.3	4.6	570.2	72.3	546.8	4.3	100.0
IM13_26	0.44	133,027.24	1054	0.26	−1611.77	−45.20	11.23	0.5	0.05751	1.19	0.064977190	1.306250	0.7057	1.1	0.08904	0.5	0.00	542.2	8.9	549.9	4.9	510.2	50.7	548.1	4.3	109.5
IM13_41	−0.24	160,436.72	1274	0.39	2326.15	56.42	11.23	0.6	0.05854	0.95	0.094449391	1.611378	0.7184	1.2	0.08905	0.6	0.60	549.7	10.1	549.9	6.2	548.9	42.3	549.9	6.2	104.3
IM13_54	−0.18	104,782.17	868	0.27	888.64	60.09	11.23	0.7	0.05858	1.31	0.071699025	2.290324	0.7191	1.3	0.08908	0.7	0.27	550.2	11.2	550.1	7.3	550.5	57.2	550.1	6.8	104.8
IM13_16	0.49	127,901.11	854	0.38	−379.70	−127.15	11.21	0.8	0.05860	1.28	0.096080793	1.117857	0.7207	1.4	0.08923	0.7	0.39	551.1	11.6	551.0	7.8	551.3	55.7	551.0	7.4	102.4
IM13_48	0.03	122,383.66	961	0.24	731.00	103.46	11.19	0.8	0.06035	2.20	0.061771237	1.989648	0.7436	2.2	0.08940	0.8	0.16	564.5	18.7	552.0	8.2	615.3	94.3	553.4	7.9	92.7
IM13_42	−0.67	100,111.59	810	0.27	774.08	70.18	11.18	0.5	0.05826	1.21	0.069183336	2.188661	0.7181	1.2	0.08942	0.6	0.27	549.5	10.4	552.1	5.9	538.7	52.5	551.7	5.7	107.7
IM13_44	−0.03	115,836.08	852	0.41	1432.47	65.84	11.17	0.6	0.05882	1.40	0.094624155	1.457772	0.7254	1.3	0.08949	0.6	0.08	553.9	11.3	552.5	6.1	559.5	61.0	552.8	5.5	102.8
IM13_23	0.22	132,400.68	1237	0.35	−779.71	−77.94	11.17	2.0	0.05792	1.77	0.078672272	2.986619	0.7148	2.8	0.08954	2.1	0.78	547.6	23.9	552.8	22.1	525.8	78.3	551.0	21.4	107.9
IM13_6	0.42	89,477.78	947	0.31	1395.99	62.19	11.17	0.7	0.06017	1.78	0.063985802	2.649602	0.7423	1.8	0.08951	0.7	0.24	563.7	15.6	552.6	7.4	608.9	76.4	553.8	7.2	94.4
IM13_9	0.40	65,994.37	621	0.24	−1965.39	−42.32	11.15	0.6	0.05919	1.83	0.064447794	4.362465	0.7319	2.0	0.08972	0.6	0.43	557.7	17.5	553.9	6.6	573.1	80.8	553.8	6.6	100.4
IM13_53	−0.26	49,261.05	418	0.32	834.03	44.95	11.14	0.7	0.05958	2.27	0.082380675	2.488174	0.7370	2.3	0.08975	0.7	0.17	560.6	19.6	554.0	7.6	587.5	98.2	554.6	7.4	104.1
IM13_17	1.38	87,767.81	578	0.38	240.40	131.51	11.14	0.9	0.05911	1.33	0.101777241	2.334647	0.7311	1.5	0.08976	0.9	0.48	557.2	13.0	554.1	9.2	570.0	58.0	554.7	8.9	99.7
IM13_36	−0.06	54,280.28	538	0.48	−731.14	−53.58	11.13	1.6	0.05801	1.84	0.120337029	2.034620	0.7182	2.2	0.08983	1.8	0.60	549.6	18.9	554.5	18.9	529.3	80.5	552.0	16.9	111.0
IM13_11	−0.23	163,860.51	1282	0.35	−3922.11	−28.20	11.14	0.7	0.06043	1.17	0.090428852	1.170878	0.7477	1.3	0.08977	0.8	0.47	566.9	11.4	554.2	8.0	618.2	50.5	556.6	7.8	90.6
IM13_20	0.41	112,039.04	723	0.40	−1102.63	−50.89	11.13	0.5	0.05873	1.18	0.103191626	1.141426	0.7273	1.2	0.08985	0.5	0.18	555.0	10.1	554.7	5.0	556.2	51.9	554.7	4.8	101.8
IM13_12	0.34	93,512.91	681	0.26	59.05	577.72	11.13	0.4	0.05798	1.23	0.065409197	1.451185	0.7183	1.2	0.08988	0.4	0.07	549.6	10.0	554.9	4.6	528.1	53.8	554.0	4.3	107.0
IM13_3	−0.13	148,766.49	1500	0.34	1503.88	64.08	11.12	0.6	0.05923	1.48	0.081113927	1.368830	0.7338	1.5	0.08990	0.6	0.19	558.8	12.6	554.9	6.6	574.5	64.1	555.6	6.2	97.3
IM13_43	−0.20	89,308.87	740	0.42	817.54	72.34	11.12	0.7	0.05818	1.37	0.107712452	1.852263	0.7211	1.4	0.08994	0.8	0.34	551.3	12.2	555.2	8.1	535.4	60.6	554.4	7.6	110.1
IM13_25	0.33	96,562.84	782	0.44	−451.12	−90.23	11.09	0.6	0.05746	1.17	0.106879351	1.328882	0.7142	1.3	0.09019	0.6	0.44	547.2	11.1	556.6	6.4	508.3	51.9	555.7	6.3	113.3
IM13_55	−0.23	90,481.69	734	0.46	526.49	67.63	11.08	0.7	0.05884	1.30	0.107549014	1.279030	0.7317	1.2	0.09023	0.6	0.09	557.6	10.4	556.9	6.8	560.2	57.4	557.1	5.9	103.9
IM13_50	0.59	113,672.47	846	0.39	−337.24	−143.96	11.07	1.8	0.06161	1.78	0.108557100	1.498952	0.7672	3.1	0.09036	2.2	0.82	578.2	27.3	557.6	23.4	659.6	76.7	558.6	23.9	90.6
IM13_7	0.11	102,662.94	983	0.29	8291.72	222.96	11.04	0.4	0.05999	1.23	0.073550934	1.271346	0.7487	1.1	0.09055	0.5	0.01	567.4	9.9	558.8	4.8	602.4	53.0	560.4	4.4	94.6
IM13_24	−0.08	160,638.02	1383	0.33	745.50	119.38	11.03	1.4	0.05910	1.58	0.084129965	1.708132	0.7382	2.0	0.09064	1.3	0.60	561.4	17.0	559.3	14.2	569.7	68.8	559.9	13.7	99.2
IM13_27	1.15	99,831.71	714	0.43	−2017.12	−79.95	11.03	0.7	0.05834	2.74	0.108375047	2.255178	0.7292	2.9	0.09069	0.7	0.39	556.1	24.9	559.6	7.7	541.6	118.7	559.7	7.6	106.5
IM13_8	0.46	120,910.30	1211	0.38	−6090.48	−44.82	11.03	0.7	0.05860	1.41	0.091002477	1.054368	0.7325	1.4	0.09070	0.7	0.20	558.0	12.0	559.7	7.4	551.2	62.3	559.3	6.8	104.3
IM13_10	0.08	128,480.70	1209	0.38	−1535.32	−77.61	11.01	0.6	0.06091	1.59	0.093252216	1.419036	0.7625	1.5	0.09083	0.6	0.02	575.4	13.2	560.5	6.2	635.0	68.9	563.0	5.6	89.1
IM13_5	0.14	119,308.67	1225	0.35	2271.39	49.07	10.99	0.6	0.06008	1.44	0.087078501	0.902088	0.7536	1.5	0.09102	0.6	0.21	570.3	12.7	561.6	6.0	605.4	62.7	562.6	5.8	94.8
IM13_29	0.21	111,713.12	889	0.34	−383.84	−118.77	10.97	0.5	0.05901	1.08	0.079388664	0.988541	0.7411	1.1	0.09113	0.5	0.23	563.0	9.1	562.2	5.8	566.4	46.6	562.4	5.4	101.7
IM13_21	−0.40	161,314.06	1256	0.38	−2162.87	−32.48	10.96	0.8	0.05862	1.15	0.088702902	1.317675	0.7371	1.4	0.09124	0.8	0.62	560.7	12.3	562.9	8.7	552.0	49.1	562.6	8.7	103.8
IM13_1	0.57	86,884.00	776	0.30	82.95	338.19	10.95	0.6	0.06001	1.27	0.083938084	3.599114	0.7550	1.5	0.09129	0.6	0.48	571.1	12.9	563.2	6.6	602.9	56.0	563.3	6.6	97.4
IM13_31	0.26	144,575.99	1668	0.40	106.18	477.09	10.95	1.1	0.05757	2.21	0.093619397	2.073641	0.7247	2.5	0.09133	1.1	0.41	553.4	21.4	563.4	11.3	512.5	100.9	562.6	11.2	116.7
IM13_39	0.03	100,297.21	849	0.27	−7731.54	−27.24	10.94	0.6	0.05741	1.17	0.070715278	1.263577	0.7234	1.1	0.09142	0.6	0.17	552.7	9.7	563.9	6.1	506.5	52.2	561.2	5.5	116.2
IM13_58	−0.20	147,215.03	1215	0.32	596.25	92.72	10.92	0.5	0.05850	0.96	0.083069719	1.540365	0.7383	1.1	0.09157	0.5	0.50	561.4	9.5	564.8	5.4	547.7	41.8	564.6	5.4	107.0
IM13_52	−0.29	69,707.24	531	0.41	1468.18	46.09	10.90	0.5	0.05805	1.55	0.107016081	2.603264	0.7339	1.5	0.09173	0.5	0.00	558.8	12.6	565.7	5.3	530.8	67.9	564.7	4.9	113.1
IM13_56	1.10	87,406.21	740	0.30	886.20	44.52	10.90	0.9	0.05745	1.58	0.078624198	1.475047	0.7266	1.5	0.09177	0.9	0.24	554.5	13.1	566.0	9.8	507.9	69.7	562.3	8.7	117.6
IM13_22	0.31	156,323.77	1311	0.41	−1604.66	−58.22	10.90	1.1	0.06023	1.11	0.103068820	2.003954	0.7617	1.4	0.09176	1.1	0.62	575.0	11.9	565.9	11.6	610.9	47.1	570.1	10.7	91.7
IM13_37	−0.52	80,362.95	763	0.46	−1991.26	−44.33	10.89	0.6	0.05757	1.56	0.099873606	1.355422	0.7285	1.6	0.09183	0.6	0.20	555.7	13.3	566.3	7.0	512.4	68.4	564.6	6.7	118.3
IM13_51	−0.20	118,399.91	932	0.38	6100.86	33.01	10.86	1.3	0.05812	1.02	0.090155355	1.802596	0.7377	1.7	0.09209	1.4	0.78	561.0	14.6	567.9	15.1	533.4	46.5	563.9	13.9	111.4
IM13_18	−0.20	117,878.12	783	0.34	−126.24	−349.95	10.81	0.7	0.05846	1.61	0.084755922	1.805144	0.7451	1.4	0.09248	0.8	0.08	565.4	12.5	570.2	8.2	546.1	68.4	568.8	7.1	105.8
IM13_45	1.74	44,565.77	325	0.35	246.15	96.17	10.80	0.7	0.06105	2.31	0.097219699	1.756498	0.7787	2.2	0.09255	0.7	−0.03	584.8	19.4	570.6	7.6	640.1	99.6	572.6	7.0	96.1
IM13_19	0.33	130,761.47	814	0.40	−339.65	−124.23	10.80	0.5	0.05964	1.09	0.098772336	0.997957	0.7612	1.3	0.09261	0.6	0.54	574.7	11.4	571.0	6.3	589.6	47.8	571.0	6.3	98.8
IM13_38	−0.18	110,061.75	956	0.20	−2590.83	−56.77	10.77	1.7	0.05788	1.68	0.049271998	1.427632	0.7410	2.4	0.09289	1.7	0.72	563.0	20.5	572.6	18.4	524.3	72.6	569.5	17.7	114.9
IM13_47	−0.51	68,121.92	528	0.21	201.43	139.60	10.75	0.5	0.05971	1.39	0.057103024	2.027474	0.7652	1.5	0.09299	0.5	0.31	577.0	13.0	573.2	5.7	592.2	61.0	573.4	5.6	102.8
IM13_14	−0.31	124,210.46	765	0.37	−969.96	−57.81	10.72	1.8	0.05818	1.59	0.091099598	2.533829	0.7483	2.3	0.09333	2.0	0.73	567.2	20.2	575.2	21.9	535.5	70.1	569.9	19.3	109.6
IM13_46	−0.51	89,226.11	686	0.34	−49.52	−460.24	10.72	0.5	0.05770	1.27	0.086775141	1.888714	0.7421	1.3	0.09332	0.5	0.23	563.7	11.2	575.2	5.4	517.5	56.0	573.7	5.2	118.2
IM13_33	−0.06	89,593.37	978	0.36	−353.36	−115.38	10.71	0.7	0.05815	1.20	0.088873497	2.804020	0.7479	1.3	0.09333	0.7	0.39	567.0	11.5	575.2	7.4	534.3	53.8	573.7	7.1	113.1
IM13_30	0.41	52,307.02	376	0.20	−620.39	−73.43	10.71	0.7	0.05944	2.62	0.048122591	2.385948	0.7647	2.4	0.09334	0.7	−0.17	576.7	21.4	575.3	8.0	582.4	114.9	575.5	7.0	105.2
IM13_4	0.59	72,465.89	741	0.26	565.16	54.49	10.71	1.0	0.05886	2.21	0.066866732	1.775229	0.7576	2.1	0.09339	1.1	0.18	572.6	18.6	575.6	12.0	561.0	96.0	574.8	10.8	106.5
IM13_57	0.25	89,756.77	743	0.21	511.45	64.57	10.67	1.9	0.05861	1.17	0.052707283	1.772673	0.7568	2.0	0.09369	1.8	0.83	572.2	17.4	577.4	19.9	551.6	48.9	572.8	17.3	108.8
IM13_32	−0.34	104,143.31	1131	0.43	−2354.77	−27.97	10.67	1.4	0.05846	1.14	0.103238028	1.054163	0.7553	1.9	0.09375	1.4	0.79	571.3	17.0	577.7	15.7	546.0	52.1	575.6	15.2	110.2
IM13_59	−0.11	87,044.51	683	0.20	213.33	162.94	10.65	0.5	0.05838	1.38	0.050685443	1.866758	0.7554	1.5	0.09389	0.5	0.33	571.3	12.9	578.5	5.3	542.9	61.0	578.2	5.3	112.2
IM13_13	0.28	110,912.19	770	0.43	−699.05	−61.21	10.61	1.2	0.05924	1.32	0.105976791	1.501405	0.7693	1.8	0.09423	1.3	0.71	579.4	16.2	580.5	14.0	574.9	56.2	580.2	13.7	104.4
IM13_2	0.97	44,639.49	419	0.23	346.72	54.14	10.58	0.6	0.05952	1.89	0.056390584	2.796483	0.7751	2.0	0.09450	0.6	0.23	582.7	17.6	582.1	7.1	585.1	84.1	582.1	6.9	107.4
IM13_28	0.14	108,327.20	804	0.48	−1388.23	−42.88	10.45	1.4	0.05779	1.33	0.110251321	1.149506	0.7622	1.9	0.09570	1.4	0.70	575.3	16.3	589.2	15.3	520.9	57.8	583.4	14.4	116.3
IM13_40	0.34	25,969.57	191	0.29	−2437.47	−32.93	10.16	0.7	0.05847	2.39	0.078128186	2.595515	0.7934	2.4	0.09846	0.7	0.06	593.1	21.2	605.4	7.9	546.5	105.8	604.0	7.5	129.4
IM13_60	−0.21	41,358.80	287	0.57	−189.01	−101.40	10.12	1.0	0.06110	2.67	0.145046360	1.762176	0.8324	2.9	0.09886	1.0	0.36	615.0	26.7	607.7	11.5	641.6	116.4	608.0	11.5	103.2

and

Table A5. LA–ICP–MS U-Pb data for the Plešovice as a secondary reference material.

						Data for Wetherill plot					Data for Tera–Wasserburg plot						Dates						Uppm	%Conc
Identifier	f206c	206Pb	Th/U	206Pb/204Pb	1s%	207Pb/235U	1s%	206Pb/238U	1s%	Rho	238U/206Pb	1s%	207Pb/206Pb	1s%	208Pb/206Pb	1s%	207Pb/206Pb	2s	206Pb/238U	2s	207Pb/235U	2s
Ples_23	0.75	53,639.15	0.10	−475.66	−55.12	0.3910	1.9	0.05333	0.7	0.14	18.75	0.7	0.05320	1.91	0.026077042	2.334217	336.1	86.3	335	4.4	335.1	10.7	755	113.2
Ples_24	0.65	51,582.22	0.10	−333.03	−59.50	0.3930	1.6	0.05398	0.5	0.15	18.53	0.6	0.05283	1.58	0.026185734	2.417102	320.5	71.5	338.9	3.6	336.6	9	753	117.0
Ples_21	−0.16	54,056.98	0.10	−710.06	−44.95	0.3849	1.9	0.05355	0.6	0.18	18.68	0.6	0.05215	1.85	0.026301091	2.096167	291.1	84.6	336.3	3.9	330.6	10.5	756	132.3
Ples_22	0.50	56,947.94	0.10	−481.16	−58.94	0.4003	1.5	0.05406	0.6	0.35	18.50	0.6	0.05372	1.42	0.026484392	2.432624	358.4	63.7	339.4	3.9	341.8	8.7	756	100.5
Ples_19	0.34	64,492.82	0.10	−717.73	−42.90	0.3862	1.4	0.05306	0.5	−0.07	18.85	0.5	0.05282	1.54	0.026989844	2.255749	320	70.4	333.3	3.4	331.6	8.1	759	110.7
Ples_20	−0.68	60,841.23	0.10	−128.01	−151.71	0.3967	1.6	0.05380	0.5	0.15	18.59	0.5	0.05351	1.57	0.027760912	2.252616	349.3	71.1	337.8	3.1	339.2	9.1	749	103.6
Ples_17	−0.13	50,483.61	0.10	−538.81	−38.77	0.4027	1.7	0.05417	0.6	0.04	18.46	0.6	0.05394	1.76	0.024589258	2.786096	367.6	78.8	340.1	4.1	343.6	9.7	761	102.4
Ples_18	0.94	45,108.48	0.10	−145.53	−91.66	0.3929	1.9	0.05352	0.6	0.16	18.68	0.6	0.05326	1.90	0.025098741	2.681902	339	85.8	336.1	4	336.5	10.9	746	113.5
Ples_15	0.22	57,762.89	0.10	3293.35	38.95	0.3978	1.8	0.05339	0.7	0.16	18.73	0.7	0.05406	1.79	0.026339451	2.085549	372.7	81.5	335.3	4.6	340.1	10.3	759	102.5
Ples_16	−0.10	56,786.00	0.10	3399.06	30.13	0.4058	1.5	0.05379	0.6	0.08	18.59	0.6	0.05473	1.60	0.026293593	2.371205	400.3	72	337.8	3.9	345.8	9	751	92.9
Ples_13	0.38	58,465.39	0.10	−3269.51	−25.66	0.3986	1.6	0.05351	0.5	0.03	18.69	0.5	0.05406	1.65	0.025898016	2.310606	372.5	74.2	336	3.2	340.7	9.2	755	100.9
Ples_14	0.87	58,262.30	0.10	−7853.69	−40.70	0.3842	1.5	0.05413	0.5	0.05	18.48	0.5	0.05150	1.58	0.030559173	3.721279	262.2	72.9	339.8	3.6	330.1	8.6	754	152.0
Ples_12	−0.53	58,000.28	0.10	−412.24	−50.33	0.3962	1.5	0.05373	0.5	0.04	18.61	0.5	0.05350	1.62	0.027386150	2.289054	349.2	73	337.4	3.6	338.9	8.9	755	106.2
Ples_9	−0.87	55,100.71	0.10	−229.31	−86.58	0.3907	1.7	0.05361	0.6	−0.03	18.65	0.6	0.05288	1.84	0.026982504	2.353171	322.6	82.5	336.6	3.8	334.9	9.7	758	114.0
Ples_10	0.35	50,624.57	0.10	181.71	103.68	0.3932	1.6	0.05346	0.6	0.00	18.70	0.6	0.05337	1.66	0.026793920	2.393834	343.4	75.9	335.7	3.8	336.7	9	750	105.5
Ples_7	−0.54	65,704.87	0.10	−1017.31	−33.47	0.3838	2.0	0.05366	0.5	0.06	18.64	0.5	0.05190	2.03	0.027179428	2.478643	280	92.8	336.9	3.6	329.8	11.2	756	140.8
Ples_8	−0.08	64,016.75	0.10	−881.40	−36.59	0.3945	1.5	0.05359	0.4	0.21	18.66	0.4	0.05342	1.48	0.026915904	2.317759	345.5	66.6	336.5	2.8	337.7	8.6	755	104.6
Ples_5	1.06	57,925.43	0.10	−378.49	−78.35	0.3958	1.9	0.05341	0.7	0.10	18.72	0.7	0.05377	1.92	0.031027944	4.375674	360.2	88.7	335.4	4.5	338.6	11	746	104.3
Ples_6	−0.21	70,445.41	0.10	−2120.34	−32.08	0.3977	1.3	0.05407	0.4	−0.05	18.50	0.4	0.05337	1.43	0.026248336	2.105787	343.4	64.8	339.5	2.9	340	7.7	764	107.5
Ples_4	0.52	53,505.12	0.10	−311.05	−66.13	0.3899	1.7	0.05365	0.5	−0.08	18.64	0.5	0.05273	1.85	0.026213515	2.597983	316.1	84.4	336.9	3.5	334.3	9.9	753	121.1
Ples_2	0.55	61,258.80	0.10	344.80	81.34	0.3948	1.5	0.05357	0.5	0.15	18.67	0.5	0.05347	1.50	0.026234842	2.470396	347.9	67.7	336.4	3.6	337.9	8.5	756	102.4

). After processing the raw data and generating U-Pb ratios, Isoplot R 1.0 [37] was used to generate U-Pb ages, draw concordia diagrams, and calculate the discordance distance and ²⁰⁶Pb/²³⁸U weighted mean ages. All error bars and reported errors in the text are at the 2σ level.

4. Results

4.1. Petrography of the Host Rocks

The host rocks comprise the Late Ediacaran magmatic suites (LEMS) of the Ouarzazate Group (580–539 Ma), which intrude the volcanic and volcanoclastic rocks of the Saghro Group (620–600 Ma) [16,29,38]. Considering their absolute ages, the LEMS in the Tifnoute Valley area comprise the Assarag, Amassine, and Ougougane suites.

4.1.1. The Assarag Magmatic Suite

The Assarag magmatic suite is represented by the Askaoun quartz diorite and amphibole-biotite granodiorite. The granodiorite is pink-colored and medium-grained rock. The primary mineral paragenesis consists of various proportions of euhedral plagioclase, quartz, and K-feldspar locally developing mermekitic and graphic textures, while biotite and amphibole occur as anhedral megacrysts (Figure 5A). Accessory minerals consist of apatite, zircon, titanite, and magnetite. Secondary minerals consist of sericite, chlorite, epidote, and kaolinite. The quartz diorite is dark grey-colored, medium to coarse-grained, and heavily altered, and its mineral paragenesis consists of mm-sized sericitized plagioclase, epidotized amphibole, chloritized biotite, and abundant quartz and opaque minerals.

4.1.2. The Amassine Magmatic Suite

This suite is represented by the large Imourkhssen granite that occurs as a star-shaped barren batholith intruded into the granodiorite of the Assarag suite. Macroscopically, the Imourkhssen granite is pinkish and coarse-grained rock. The primary mineral paragenesis comprises perthitic K-feldspar (≃30%), albite-oligoclase (≃30%), along with quartz (≃35%) and chloritized biotite (˂5%) (Figure 5B). Accessory minerals contain magnetite, apatite, and zircon, while the secondary mineral assemblage consists of sericite, chlorite, and kaolinite.

4.1.3. The Ougougane Magmatic Suite

This suite consists of a series of rhyolitic, microgranitic, and granitic intrusions cutting across both the Amassine and Assarag suites. The rhyolite exhibits pyromerides in the form of radiant fibers of orthoclase surrounding a quartz nucleus and displaying a distinguishable hyaline spherulitic texture. Accessory minerals consist of zircon, rare apatite, and Fe-oxides, while sericite and chlorite are the secondary minerals.

The microgranite occurs as pink-colored and fine-grained dykes. Its mineralogy consists of a significant proportion of interstitial quartz, perthitic K-feldspar, and albite-oligoclase displaying locally a well-developed mermekitic texture. Biotite and opaque minerals are observed as accessory minerals within the microgranite.

The granite of the Ougougane suite, including the nearby Imourgane intrusion, occurs as a pinkish and coarse-grained to porphyritic granite (Figure 5C). The mineral paragenesis consists of quartz and K-feldspar displaying a graphic texture. The feldspars are commonly hydrothermally altered to sericite and/or kaolinite. Muscovite is rarely observed, whereas biotite is ubiquitous. The latter is commonly altered to chlorite and exhibits numerous inclusions of apatite, zircon, and opaque minerals.

4.1.4. The Zaghar Mafic Dykes

The Zaghar mafic dykes consist of a swarm of doleritic dykes (2 to 15 m thick) that intrude the LEMS. These dykes are fine to medium-grained, olive green in color, and have intersertal ophitic textures. The primary mineralogy of some dykes consists of plagioclase laths, while the Fe-Mg minerals are often transformed to chlorite and epidote. Nevertheless, some dykes contain many phenocrysts of clinopyroxene exhibiting the glomeroporphyritic texture (Figure 5D).

Figure 5. Selected photomicrographs of the LEMS at XPL (cross-polarized light) with the Askaoun granodiorite in (A), the Imourkhssen granite in (B), the Imourgane granite in (C) and the Zaghar mafic dyke in (D). Mineral abbreviations: Opq: opaque, Amp: amphibole, Qz: quartz, Chl: chlorite, Bt: biotite, Kln: kaolinite, K-Fsp: K-feldspar, Or: orthoclase, Cpx: clinopyroxene, Sr: sericite, Pl: plagioclase, Zrn: zircon.

Figure 5. Selected photomicrographs of the LEMS at XPL (cross-polarized light) with the Askaoun granodiorite in (A), the Imourkhssen granite in (B), the Imourgane granite in (C) and the Zaghar mafic dyke in (D). Mineral abbreviations: Opq: opaque, Amp: amphibole, Qz: quartz, Chl: chlorite, Bt: biotite, Kln: kaolinite, K-Fsp: K-feldspar, Or: orthoclase, Cpx: clinopyroxene, Sr: sericite, Pl: plagioclase, Zrn: zircon.

Locally, the Zaghar dyke swarm shows co-mingling magmatic textures at contact with the Askaoun granodiorite of the Assarag suite (Figure 6), suggesting their simultaneous emplacement. Similar textures have also been documented in the Zaghar mafic dyke swarms located in Douar Eç-çour, north of the studied area [39]. Geochronological dates have not been reported in the Imourkhssen area. However, a zircon/apatite/rutile U-Pb age of 554 ± 6 Ma was documented from a dolerite dyke in the Douar Eç-çour [39].

4.2. Whole-Rock Geochemistry

Seventeen representative samples of the LEMS were analyzed for major and trace elements, as shown in Appendix A, Table A2.

The rocks of the Ougougane suite, including the Imourgane granite, exhibit high SiO₂ content (72.39–77.02 wt%) and medium total alkali content (K₂O+Na₂O) within the range of 8.27 wt%. They fall into the granite field on the total alkalis versus SiO₂ diagram (Figure 7A). The A/CNK values [Al₂O₃/(CaO+Na₂O+K₂O)] of these samples are from 1.34 to 1.67, whereas the A/NK values [Al₂O₃/(Na₂O+K₂O)] range from 1.38 to 1.72, indicating a peraluminous composition (Figure 7B).

The spidergrams (Figure 7E) of these rocks are generally parallel and typical to calc-alkali series with enrichments in LILEs (large ion lithophile elements, K to Th), in addition to large Sr, Ba, P, and Ti negative anomalies. These anomalies can be explained by feldspar (Sr and Ba) and accessory mineral fractionation and accumulation in the source as apatite (P) and titanite (Ti), whilst the Nb anomaly is likely to be characteristic of the melt source (See discussion section). Their chondrite-normalized REE (rare earth element) patterns (Figure 7F) also show calc-alkali trends alongside a slight Pr negative anomaly in many samples. The rocks display a fractionated LREE and flat HREE patterns in addition to a notable Eu anomaly.

The Askaoun batholiths of the Assarag suite are distinctive due to their high Fe₂O₃(T) contents, oscillating between 7.76 and 9.01 wt% and between 4.1 and 5.57 wt% for the quartz diorite and the granodiorite, respectively. The silica contents vary from 57.4 to 66.54 wt%. The A/CNK ratios of 1.37–2.90 indicate a peraluminous characteristic (Figure 7B). Their spidergrams and REE patterns are close to those of the Ougougane suite, with less pronounced Sr, Ba, P, Nb, Ti, and Eu negative anomalies.

Though their Nb-Ta arc signature, the LEMS samples straddle the post-orogenic field in the Rb versus (Y+Nb) tectonic discrimination diagram (Figure 7D). Their Harker diagrams show negative correlations between SiO₂ and MgO, FeO, CaO, TiO₂, Sr, and V, and positive correlations with K₂O, Rb, and Th (Figure 8). Such compositional variations of the rocks could be produced by different amounts of crystal fractionation [40].

The LEMS of the Tifnoute Valley area plot in the high potassic calc-alkaline series in the K₂O versus SiO₂ diagram (Figure 7C), as already mentionned in [29]. They exhibit a peraluminous composition and lack Al-rich minerals (e.g., muscovite, cordierite, and garnet). This geochemical feature is consistent with an I-type affinity [29], which is portrayed as well by the Nd and Sr isotope values (εNd − 560 Ma + 0.8 and + 3.5 with (⁸⁷Sr/⁸⁶Sr)i between 0.7034 and 0.7065 [29]) (Figure 9B), pointing to a mainly juvenile source (mantle or young lower crust) [29].

The negative correlation between SiO₂ and P₂O₅ (Figure 9A) also suggests an I-type granite trend [41] for the LEMS. Those authors suggest that this I-type granite evolution implies the potential origin of the magma through the partial melting of metaigneous rocks.

The entire geochemical characteristics of the LEMS is typical of post-collisional magmas [42]. Those magmas have been emplaced in the framework of the Late Ediacaran collapse of the Pan-African orogen [21,28].

Figure 7. Whole-rock geochemistry of the Late Ediacaran granites of the TV area. (A) Total alkali (Na₂O + K₂O) (wt%) versus SiO₂ (wt%) diagram after [43]. (B) A/NK versus A/CNK diagram of [44]. (C) SiO₂ vs. K₂O diagram after [45]. (D) Tectonic discrimination Rb vs. Y+Nb diagram after [46,47]. Abbreviations: syn-COLG: syn-collisional granite, WPG: within plate granite, POG: post-collisional granite, VAG: volcanic arc granite, ORG: oceanic ridge granite. (E,F) Primitive mantle-normalized trace-element spidergram and chondrite-normalized REE distribution diagrams of TV magmatic rocks compared to previous trends in [29], shown as grey trends. The MORB values are from [48], and the chondrite values are from [45].

Figure 7. Whole-rock geochemistry of the Late Ediacaran granites of the TV area. (A) Total alkali (Na₂O + K₂O) (wt%) versus SiO₂ (wt%) diagram after [43]. (B) A/NK versus A/CNK diagram of [44]. (C) SiO₂ vs. K₂O diagram after [45]. (D) Tectonic discrimination Rb vs. Y+Nb diagram after [46,47]. Abbreviations: syn-COLG: syn-collisional granite, WPG: within plate granite, POG: post-collisional granite, VAG: volcanic arc granite, ORG: oceanic ridge granite. (E,F) Primitive mantle-normalized trace-element spidergram and chondrite-normalized REE distribution diagrams of TV magmatic rocks compared to previous trends in [29], shown as grey trends. The MORB values are from [48], and the chondrite values are from [45].

Figure 8. Harker diagrams of selected major oxide and trace elements content of the Late Ediacaran granites of the TV area. The proximal evolutionary trends are highlighted by the grey arrows.

Figure 8. Harker diagrams of selected major oxide and trace elements content of the Late Ediacaran granites of the TV area. The proximal evolutionary trends are highlighted by the grey arrows.

Figure 9. (A) P₂O₅ vs. SiO₂ classification diagram after [49]. Data for geochemical trend are from this study. (B) Sr and Nd isotopic initial ratios (εNd vs. (⁸⁷Sr/⁸⁶Sr)i at 570 Ma for the TV magmatic rocks from [29], I-type granite values from [50].

Figure 9. (A) P₂O₅ vs. SiO₂ classification diagram after [49]. Data for geochemical trend are from this study. (B) Sr and Nd isotopic initial ratios (εNd vs. (⁸⁷Sr/⁸⁶Sr)i at 570 Ma for the TV magmatic rocks from [29], I-type granite values from [50].

4.3. X-ray Data

XRD analyses were carried out for the identification of various primary and secondary mineral assemblages in several samples, especially those related to alteration zones (Figure 10). Indeed, the serecitic mineral assemblages (i.e., 22im05) is composed mainly of quartz and sericitized feldspars. The Imourgane granite (i.e., 22im02) is composed of quartz, feldspar, biotite, and muscovite. Furthermore, X-ray primary investigations delineate the quartz-chlorite-sulfide assemblages (i.e., 22im17 and 22im13C), which form the ore-bearing structures (see mineralization section). The pervasive silica enrichment within the Imourgane granite is also outlined (i.e., 22im20). It impacts the outcrops near the galleries, where epsomite (MgSO₄·7H₂O) encrustations can be found (i.e., T1). This mineral was recently discovered to be useful for geochemical classification [51].

4.4. Hydrothermal Alteration and Veining System

4.4.1. Hydrothermal Alteration

Field observations and petrographic examination allowed us to identify several hydrothermal alteration assemblages, including (i) potassic, (ii) chlorite-sericite, (iii) serecitic, and (iv) propylitic alteration.

(i) The potassic alteration affects the Imourgane granite and exhibits disseminated molybdenite and molybdenite veinlets (Figure 11A). This alteration is highlighted by the characteristic brick red color of secondary K-feldspars, locally crossed by stockworks of chlorite. The altered feldspar to clay minerals (kaolinite), along with quartz, chlorite, and altered biotite, make up the potassic alteration mineral assemblage.

(ii) The chlorite-sericite alteration surrounds the potassic alteration zone. It occurs as grey dark halos surrounding disseminated molybdenite (Figure 11B). This alteration consists of chloritized biotite crystals along with quartz and sericitized plagioclase.

(iii) The serecitic or phyllic alteration overprints a large area of the Imourgane granite, as evidenced by the large, bleached zones (Figure 11C) extending over tens of square meters. It consists of quartz and sericite along with pervasive pyritization and silicification.

(iv) The propylitic alteration consists of chlorite alteration halos along with epidote and local calcite (Figure 11D).

Figure 11. Photomicrographs of the hydrothermal alteration mineral assemblages with associated samples. (A) Potassic alteration highlighted by brick red-colored K-feldspar and molybdenite (Mol) dissemination within the Imourgane granite. (B) Chlorite-sericite alteration with molybdenite dissemination. (C) Phyllic or sericitic alteration highlighted by bleached outcrops. (D) Propylitic halo within the Imourgane granite along with molybdenite dissemination. Mineral abbreviations: K-Fsp: K-feldspar, Chl: chlorite, Mol: molybdenite.

Figure 11. Photomicrographs of the hydrothermal alteration mineral assemblages with associated samples. (A) Potassic alteration highlighted by brick red-colored K-feldspar and molybdenite (Mol) dissemination within the Imourgane granite. (B) Chlorite-sericite alteration with molybdenite dissemination. (C) Phyllic or sericitic alteration highlighted by bleached outcrops. (D) Propylitic halo within the Imourgane granite along with molybdenite dissemination. Mineral abbreviations: K-Fsp: K-feldspar, Chl: chlorite, Mol: molybdenite.

4.4.2. Veining System

The predominant strike orientation of veins and their controlling faults are of NNE–SSW to N–S directions. In the studied area, several vein types are recognized and can be categorized into four types: (i) Aplitic mega lenses, (ii) stockwork-type quartz veins, (iii) quartz-hematite-barite veins, and (iv) quartz-chlorite-sulfide lenses.

(i) The aplitic mega lenses occur as N–S oriented structures within the Imourgane granite (Figure 12A). These structures consist mainly of quartz, sericitized k-feldspars, and plagioclase with minor disseminated pyrite. The aplitic lenses extend for several meters, especially in the sericitized areas.

(ii) Stockwork-type quartz veins are shown in Figure 12B and are characterized by anastomosing quartz networks affecting the Imourgane granite. These veins occur more frequently within the altered potassic and serecitic bleached zones.

(iii) Quartz-hematite veins manifest as decimetric veins (Figure 12C) that evolve to barite-hematite veins exclusively in the Imourgane granite (Figure 12D). The evolution from quartz-hematite to baryte-hematite assemblages could be the result of quartz transformation to baryte during cooling of the hydrothermal solutions, if the fluid’s composition and the physical conditions (T, P) allow it (see [54]). The barite-hematite vein zonation is observed on the small scale, creating a centimetric-sized cockade texture. Thus, an active pulsating process during ore deposition is suspected [55].

(iv) Quartz-chlorite-sulfide lenses occur as NNE–SSW to N–S trending ore-related structures (Figure 12E,F), which affect mainly the Askaoun granodiorite and the Imourgane granite. These structures exhibit crack-and-seal and cockade textures (Figure 13A) along with hydrothermal breccia (Figure 13B), highlighting multiple episodes of fluid circulation [6].

Figure 12. The different hydrothermal vein types observed in the studied area: (A) Aplite mega-lens surrounded by the bleached zone. (B) Quartz stockworks. (C) Quartz-hematite lens. (D) Barite-hematite lens out crops in phyllic alteration zone. (E,F) Quartz-chlorite sulfide lenses.

Figure 12. The different hydrothermal vein types observed in the studied area: (A) Aplite mega-lens surrounded by the bleached zone. (B) Quartz stockworks. (C) Quartz-hematite lens. (D) Barite-hematite lens out crops in phyllic alteration zone. (E,F) Quartz-chlorite sulfide lenses.

Figure 13. (A) Cockade texture in a centimetric barite-hematite vein observed within the Imourgane granitic intrusion. (B) Hydrothermal breccia affecting the quartz-chlorite-sulfide lens in a gallery of the Talat nl’bour area. Mineral abbreviations: Chl: chlorite, Qz: quartz, Hm: hematite, Brt: barite.

Figure 13. (A) Cockade texture in a centimetric barite-hematite vein observed within the Imourgane granitic intrusion. (B) Hydrothermal breccia affecting the quartz-chlorite-sulfide lens in a gallery of the Talat nl’bour area. Mineral abbreviations: Chl: chlorite, Qz: quartz, Hm: hematite, Brt: barite.

4.5. The Imourkhssen Porphyry-Style Mineralization

The ore genesis of the Imourkhssen Cu±Mo±Au±Ag deposit can be divided into supergene and magmatic-hydrothermal periods, comprising primary dissemination and secondary NNE–SSW to N–S ore-bearing system stages (Figure 14). The molybdenite occurrences and Fe-Cu disseminated sulfides belong to the primary ore stage, while the NNE–SSW to N–S quartz-chlorite-sulfide-bearing system is assigned to the secondary ore stage (Figure 15).

(i) The molybdenite is exclusively enclosed by the small elongated Imourgane granite. It occurs as fine-grained disseminations or fine flake aggregates in the potassic and the chlorite-sericite alteration zones (Figure 15A and Figure 16A) or even as centimetric veinlets within the propylitic halos (Figure 16B). Microprobe analysis of the two molybdenite types shows different geochemical compositions (Figure 17, Appendix A, Table A3), suggesting that the molybdenite was remobilized during multiple fluid circulation events.

(ii) Fe-Cu sulfide disseminations occur as patchy pyrite, chalcopyrite, galena, and tennantite mineralization in the Askaoun granodiorite (Figure 15B) and the Imourgane granite. The chalcopyrite is encased by pyrite, and exhibits itself galena inclusions (Figure 15C). The tennantite is enclosed by calcite veins, while scarce barite and bornite crystals are evidenced by scanning electron microscopy within a Zaghar doleritic dyke sample (Figure 15D).

(iii) The NNE–SSW to N–S quartz-chlorite-sulfide-bearing system is well developed in the Talat nl’bour area, where it is hosted mainly by the Askaoun granodiorite. It affects less strongly the Imourgane granite, for which scarce traces of silver have been imaged by scanning electron microscopy analysis in thin chenguodaite minerals (Figure 15F). Overall, the post mineral assemblage is formed by secondary chalcopyrite exhibiting sphalerite and pyrite inclusions (Figure 15E). The bornite, digenite, and covellite occur as replacement phases as small veinlets, filling thin fractures or around the primary minerals, while gold traces have been previously documented in [16]. Those ore-related systems displaying crack-and-seal and cockade textures and a hydrothermal breccia along NNE–SSW to N–S trends suggest multiple episodes of fluid circulation (see veining system section). The supergene stage is achieved by the mineral assemblage composed of hematite, azurite, malachite, barite, chrysocolla, and epsomite.

Figure 16. (A) Molybdenite dissemination within the Imourgane granite. (B) Molybdenite veinlets within a propylitic halo. Abbreviation: Mol: molybdenite.

Figure 16. (A) Molybdenite dissemination within the Imourgane granite. (B) Molybdenite veinlets within a propylitic halo. Abbreviation: Mol: molybdenite.

Figure 17. Quantitative results for molybdenite dissemination (MD) and molybdenite veinlet (MV) powdered samples.

Figure 17. Quantitative results for molybdenite dissemination (MD) and molybdenite veinlet (MV) powdered samples.

4.6. LA–ICP–MS U/Pb Zircon Dating

The ore-bearing Imourgane granite was previously thought to be part of the star-shaped barren Imourkhssen granite. To clarify the ages and the timing of the associated porphyry mineralization, U-Pb geochronology was conducted on both granites. The J23IM09 sample represents the Imourgane granite, while the J23IM13 sample was collected from the star-shaped barren granitic intrusion of the TV area (the Imourkhssen granite). One hundred and two zircon grains were collected for LA–ICP–MS (laser ablation–inductively-coupled plasma–mass spectrometry) U-Pb dating. Most of the zircons were euhedral and prismatic, with rare elliptic ones. CL images show mostly a homogeneous texture with some oscillatory zoning (Figure 18). Many zircon grains exhibit titanite inclusions along with sharp edges.

The age interpretations and calculations are performed using all of the zircons that are concordant within error (Appendix A, Table A4; Figure 19). The ages of the Imourkhssen and the Imourgane granites show a homogeneous distribution and can be subdivided into three classes: (i) An older generation with ages over ca. 580 Ma. These ages are considered to be inherited from the superimposed Saghro Group and older formations. (ii) A younger generation yielding scattered ages less than 550 Ma, which we interpret as resulting from Pb loss and likely due to the hydrothermal alteration recognized in the Imourkhssen area. (iii) The remaining concordant analyses are used for the concordia and weighted mean ²⁰⁶Pb/²³⁸U age calculations. Nineteen zircons for the Imourgane granite (J23IM09) yielded an age of 550 ± 2 Ma, while thirty-nine zircons from the Imourkhssen granite (J23IM13) yielded an age of 558 ± 1 Ma.

5. Discussion

5.1. Timing of the Plutonic Magmatism

The previous geochronological data reveal the existence of at least three granitoid intrusions corresponding to three magmatic pulses during the Late Ediacaran, one of which contains the Cu±Mo±Au±Ag Imourkhssen deposit [29,33,38]. The time sequence of this magmatism is described below.

5.1.1. The Askaoun Granodiorite

The Askaoun granodiorite is dated at 575 ± 8 Ma (SHRIMP method) [21], with a similar age of 575 ± 2 Ma reported in [32]. LA–ICP–MS zircon U-Pb dating in [29] yielded younger ages of 558 ± 2 Ma and 558 ± 6 Ma. On the other hand, an additional SHRIMP U-Pb zircon study provided both an older age of 579 ± 7 Ma and a zircon/apatite/rutile U-Pb younger age of 554 ± 6 Ma for the same granodiorite outcropping in the douar Eç-çour area [39] (the northeastern part of the studied area). These ages provide evidence of the multi-stage feature of the Askaoun granodiorite.

Based on a geochronological compilation of ages published throughout the Saghro domain, as defined in [30], the Ouarzazate Group (OG) seems to have been emplaced over three pulses [32]. In this paper, we propose that the initial magmatic pulse (1st flare-up) of the OG took place around ca. 575 Ma. This age announces the beginning of the deposition of the OG and the minimum age of the collision event [32,38]. In the TV area, [32] documented the same age within error from a rhyodacitic ignimbrite (577 ± 3) and a rhyolitic flow (574 ± 3 Ma) at the bottom of the volcanic series. Similar U-Pb ages within error have been measured from the Bas Drâs inlier for the Taourgha granite (575 ± 2 Ma; [56]). In the Saghro massif, this age was reported for a rhyolitic tuff and for the Wizergane granodiorite (574 ± 7 Ma and 577 ± 6 Ma, respectively; [57]), as well as for the Igoudrane granodiorite (575 ± 10 Ma; [58]) and Bou Teglimt granite (576 ± 4 Ma; [59]). In the Siroua massif, a similar age was reported in [33] for a rhyolitic plug (578 ± 4 Ma) and in [21] for the Tourcht diorite (579 ± 7 Ma), a rhyolite from the Tikhfist Formation (571 ± 8 Ma), the Aguins member (577 ± 8 Ma), and the Tilsakht granite (579 ± 7 Ma). In the Zenaga inlier, a rhyolitic ignimbrite and the Tilsakht granite have been dated at 575 ± 3 Ma and 579 ± 7 Ma in [60] and [21], respectively. In the Sidi Ifni Inlier, it has been considered that the earliest magmatic event occurred at ca. 590 Ma [30]. This was evidenced by the emplacement of the Taoulecht and Tirhite intrusions.

5.1.2. The Imourkhssen Granite

A SHRIMP U-Pb zircon study of the Imourkhssen granite produced an age of 562 ± 5 Ma [21]. In addition, an age of 561 ± 3 Ma was obtained using LA–ICP–MS U-Pb dating of zircon [29]. The LA–ICP–MS U-Pb zircon dating conducted in this study yielded an age of 558 ± 1 Ma for the Imourkhssen granitic intrusion of the TV area.

This age of approximately 560 Ma could correspond to the 2nd pulse of the OG magmatism that is also reported in many inliers of the Anti-Atlas belt. In the Sirwa inlier, an andesitic tuff is dated at ca. 562 ± 1 Ma [32]. This tuff contains inherited zircons exclusively from the Saghro Group (<610 Ma), as is the case with the Imourkhssen granite. The ignimbrite of Sirwa had also been dated in [61] at 563 ± 5 Ma. The ages of 558 ± 2 Ma and 558 ± 6 Ma obtained for the Askaoun in [29] could be assigned to the second pulse of the OG. A nearly synchronous age of ca. 560 Ma is reported in the Bas Draâ inlier in [56] for the Tarçouate gabbro-diorite (560 ± 2 Ma). In the Ighrem inlier, the Ighrem tuff, Minount rhyodacite, and Houssi El Gah rhyolitic are dated at 564.6 ± 3.2 Ma, 562.89 ± 0.49 Ma, and 560.0 ± 2.1, respectively [62]. A rhyolitic ignimbrite in Tagragra of Tata yielded the same average age (565 ± 7 Ma; [63]). Similar ages are reported in the Agadir-Melloul inlier, with many rhyolitic domes yielding an age bracket between 567 Ma and 564 Ma [64]. In the Saghro inlier, the age of 560 ± 5 Ma was reported for a mineralized halo of the Imiter deposit [65]. Geochronological dating in [66] yielded an age of 566 ± 20 Ma for the Isk-n-Alla granite, while dating in [57] yielded an age of 559 ± 5 Ma for the same granite. The Ikniwn pluton records an age of 564 ± 6 Ma [67]. Similar ages are reported in [30] for the volcanic and plutonic rocks in the Ifni inlier (e.g., the Mesti monzogranite at 567 ± 4 Ma and the Ifni syeno-granite at 566 ± 4 Ma).

5.1.3. The Ougougane Granite

The Ougougane granite yielded a LA–ICP–MS zircon U-Pb age of 550 ± 1.5 Ma [32]. This age had been interpreted as the zircon crystallization age. In this study, geochronological dating was performed on the ore-bearing granite that had been formerly assigned to the Amassine suite. LA–ICP–MS U-Pb dating on zircon yielded an age of 550 ± 2 Ma for the mineralized granite, leading to its affiliation being constrained within the Ougougane suite, and it was subsequently renamed as the Imourgane granite.

Similar ages are documented in many inliers of the Anti-Atlas (ca. 550 Ma) and could correspond to the 3rd pulse of the OG. In the Ougnat inlier, the Bou Madine rhyolitic has been dated at 552 ± 5 Ma in [28] and at 553 ± 16 Ma in [65]. In the Saghro inlier, the Takhatert and Tachkakacht rhyolites have been dated at 550 ± 3 Ma and 547 ± 8 Ma, respectively [65]. This period could be correlated with regional events that occurred through the whole Anti-Atlas, mainly the transition from a transpressive to transtensive tectonic regime by the orogenic collapse [65].

5.2. Ore Genesis and Source in the Framework of the Geodynamic Context of the Anti-Atlas

To reconstruct the magmatic-hydrothermal processes responsible for the Imourkhssen Cu±Mo±Au±Ag ore deposit, the regional geodynamic context has to be considered. As clearly reported in [16], the ore genesis of the Imourkhssen deposit is linked to the emplacement of the LEMS. This period is clearly correlated with the huge metallogenic activity associated with the highly silicic magmatism of the Ouarzazate Group. During this epoch, a large volume of juvenile material, precious metals, and chalcophile elements was added to the continental crust all over the Pan-African Anti-Atlas belt system [28,68,69]. Therefore, numerous deposits in the Moroccan Anti-Atlas, particularly in the Saghro domain, as defined in [30], seem to be affected by this magmatic event. This magmatic manifestation triggered pervasive hydrothermal activity and gave rise to world-class epithermal mineralization and base metal porphyry deposits (e.g., Imiter and Zgounder (Ag-Hg), Bou-Azzer (Co-Ni-As-Ag-Au), Iourirn (Au), and Bou Ma-dine (Cu-Pb-Zn-Au-Ag) [27,28].

In the OSS, the LEMS shows a high potassic calc-alkaline I-type granite affinity, with enrichment in LILE, relative depletion in HFSE, and a pronounced Nb-Ta anomaly. These geochemical features are akin to rocks derived from subduction-related sources [70]. Nevertheless, this signature is considered to be an inherited signature, transferred to the igneous rocks during the remelting of the subduction-related lithosphere [71]. Therefore, the emplacement of the LEMS invokes the contribution of a recycled subduction-related component [27,29]. This component could be involved in the ore enrichment, as indicated by several studies, especially for Mo and Au mineralization [72]. Its significant role is due to the H₂O, CO₂, and Cl provided from the subducted material, which ultimately contributes to the enhancement of associated hydrothermal systems [1].

In general, the ore source for porphyry copper deposits is still debated. However, a crustal component is widely invoked for the genesis of fertile sulfide rich magmas. The authors of [73] suggested that the Gattar fertile magmas originated from an underplated crustal source that was fertilized by metasomatized underplating mantle derived melts. This magmatism was responsible for the molybdenite bearing granitic intrusions in the northern Eastern Desert of Egypt. The authors of [74] assumed that the mineralization of the fertile Yulong porphyry copper deposit (eastern Tibet) originated from an eclogitized sulfide-rich juvenile lower crust melt. These melts were fueled by the injection of an ultrapotassic subduction-related metasomatized subcontinental lithospheric mantle-derived melt. The authors of [75] presumed the melting of the lower crust for the Mo enrichment, whilst the copper was suggested to be sourced from mantle melts, including subducted slab. Nevertheless, the authors of [76] assumed that Mo is more enriched in reduced sediment. In this regard, the authors of [77] associated the Mo enrichment of the porphyry Mo-Cu Pınarbaşı system (Western Turkey) with the melting of terrigenous sediment, or at least the melting of the lower crust and metasomatized mantle by subducted sediment-derived fluids.

Analogous with the observations made in [77], the Imourkhssen porphyry mineralization seems to contains a terrigenous component. The chondritic Zr/Hf ratios of the Assarag suite are scattered within the range of crustal material (32–37), while the rocks of the Ougougane suite show low Zr/Hf ratios (26–32). This feature highlights its fractionated origin [78]. Chondritic values of Zr/Hf are from [78]. Moreover, the ages of many inherited zircons (ca. 720–630 Ma) of the Imourkhssen and Imourgane granites correspond with the subduction episode that occurred in the Anti-Atlas during the Pan-African orogeny. Therefore, the LEMS could have originated from melts that include recycled subducted sediments.

The emplacement of the LEMS is contemporaneous with the widespread and huge volcanic Ouarzazate Group and its subsequent intense hydrothermal activity. This thermo-magmatic event occurred in a trans-tensional tectonic regime, corresponding with the post-collisional stage of the Pan-African orogeny that evolved toward extension during the Cambrian [27,28]. In this context, the uprising of the asthenospheric mantle close to the Moho generated a high regional heat flow that fueled the melting of the lithospheric or even the asthenospheric mantle itself [29], in addition to the lower crust with the incorporated recycled juvenile sulfide rich subduction components.

The contribution of mafic components could also be discussed for enabling sulfur and metal element enrichment to the parental magma [1]. We can assess the likely involvement of the Zaghar mafic dykes on Imourkhssen ore genesis using the following observations: (i) Many porphyry ore deposits record the associations of rhyolites of bimodal basalt-rhyolite suites [79]. (ii) The Zaghar mafic dykes of the studied area have a coeval magmatic feature with the Late Ediacaran granitoids elucidated by co-mingling structures. (iii) Disseminated mineralization is observed within the Zaghar dykes in the Imourkhssen area. These observations lead us to assume the possible contribution of this mafic component in the evolution of the Cu±Mo±Au±Ag Imourkhssen porphyry mineralization.

The multi-pulse character of the Askaoun pluton, evidenced by older and younger ages, by new geophysical data interpretations [80], and the proximity of the dated samples in [29] to the studied area, lead us to constrain the age of the mineralized granodioritic rocks of the Askaoun pluton at ca. 558 Ma. Consequently, the Imourkhssen Cu±Mo±Au±Ag porphyry-style mineralization is considered to be associated with the emplacement of the Askaoun granodiorite (ca. 558 Ma) and the Imourgane granite (ca. 550 Ma), which are coeval with the 2nd and 3rd magmatic pulses of the Ouarzazate SLIP (see Section 5.3). Field observations and detailed analysis of the Imourkhssen mineralization led us take into account the following issues:

• All the Late Ediacaran granitoids follow the same trend as mentioned in Section 4.2. Thus, these rocks belong to a single parental magma that evolved progressively and gave rise to multiple pulses and became more fractionated and differentiated over time (i.e., Ougougane suite).
• Secondly, we should contemplate the specific mineralization style of the Imourkhssen district. The Cu sulfide mineralization occurs mainly within the Askaoun granodiorite. This pluton contains a high metal grade of 0.30% and 22 g/t for Cu and Au, respectively [16]. In this framework, the probable contribution of the Zaghar mafic dykes to the Cu and Au mineralization could be envisaged because of their co-magmatic feature with the Askaoun pluton.
• Likewise, we should note that the molybdenite occurrences are restricted to the more felsic Imourgane granite, which is widely known for porphyry mineralization (e.g., similar to Mamut, East Malaysia) [81]. These observations imply not only late molybdenite precipitation but also a spatial shift from the Cu-Au bulk [1]. This feature is ideally portrayed by the Mo occurrences in the Imourgane granite and the well-developed Askaoun Cu-Au mineralization. The described shift between Mo and Cu-Au mineralizations could be related to the increasing Mo/Cu ratio in the residual parental melt, as proposed in [82].
• The importance of scarce silver is mitigated due to the lack of information. More insights could be drawn from Pb-S-O-C isotopic analysis, Re content in molybdenite, as well as from the gaseous and aqueous compositions of fluid inclusions in quartz. These analyses would be very helpful to understand the low silver concentrations here.

5.3. Late Ediacaran Ouarzazate SLIP and Implications for the Anti-Atlas Mineralization

Large igneous provinces (LIPs) are defined as large volume (>0.1 million km³) encompassing mafic rocks, with their plumbing systems, emplaced within an intraplate setting in a single pulse of short duration (˂5 Ma) [83]. Nonetheless, LIPs may contain multi-pulses of magmatism that extend over a period of less than 50 Ma [84]. In continental margins, LIPs can also be associated with silicic magmatism and, in these cases, they are referred to as silicic large igneous provinces (SLIPs) [85].

During the Late Ediacaran episode, huge silicic magmatic activity took place in the Anti-Alas belt of Morocco [28]. This magmatism has been more recently bracketed between 575 and 540 Ma and gathered under a litho-structural unit referred to as the Upper Complex in [15]. Those authors assume that throughout this timeframe (575–540 Ma), the whole Anti-Atlas belt witnessed a long-lived tectono-magmatic event evolving from high-K calc-alkaline (575–550 Ma) to alkaline (550–540 Ma) affinity, which is also reported in [86,87] in the Saghro inlier. This magmatism is thought to belong to a continental silicic large igneous province (SLIP), defined in [30] as the Ouarzazate SLIP, and emplaced over multiple pulses at ca. 575 Ma, ca. 560 Ma, and ca. 550 Ma [33] (Figure 20).

Various studies have outlined the significant role of LIPs for several metallogenic systems. LIPs are commonly related to a wide variety of metal deposits [84] and could represent the source of metals and energy for hydrothermal systems [83]. The emplacement of LIPs could provide copper and other metals for several ore deposit types, including iron-oxide-copper-gold (IOCG) and volcanogenic massive sulfide (VMS), potentially with Au deposits [84]. Nevertheless, the epithermal Au- and Carlin-type mineralizations appear to be more related to SLIPs [88].

In this regard, the authors of [28] assumed that the long-lived silicic magmatic activity of the Ouarzazate SLIP was accompanied by a pervasive hydrothermal and metallogenic manifestations. Additionally, the authors of [15] suggested possible relationships between many ore deposits and magmatic systems with multiple magmatic pulses (flare-ups) and their associated hydrothermal systems, such as Qal’at MGouna district Au-Ag (Cu, Mo, Bi, Te), including the Ismlal Au(-Cu-Mo) porphyry, Zone des Dykes Au-base metal, Thaghassa Au-Ag, Imiter Ag-Hg-Pb, Bouskour Ag-base metal, Tiouit Au-Ag-Cu, Sidi Flah Cu-Au-Ag, Tagmout Cu-Ag, and Bou Madine Au-Ag-base metal deposits (Figure 21).

In the TV area, we suggest an earlier emplacement of the first magmatic pulse generating the Askaoun granodiorite at 575 Ma (Figure 19). The age obtained in [29] (ca. 558 Ma) for this pluton outlines its extended emplacement until the second magmatic pulse (ca. 560 Ma), during which the large barren Imourkhssen intrusion was formed. The third magmatic pulse is considered to be the last manifestation of the Ouarzazate magmatic activity [32]. It spans around 550 Ma and corresponds with the emplacement of the Ougougane suite, including the Imourgane ore-bearing porphyry granite. These intrusions developed a spherulitic texture, highlighting fast cooling under low-temperature conditions [89].

Figure 20. The emplacement of the Late Ediacaran magmatic suites (LEMS) related to the three magmatic pulses of the Ouarzazate SLIP [15,33] and the position of the Imourkhssen and many ore deposits of the Anti-Atlas.

Figure 20. The emplacement of the Late Ediacaran magmatic suites (LEMS) related to the three magmatic pulses of the Ouarzazate SLIP [15,33] and the position of the Imourkhssen and many ore deposits of the Anti-Atlas.

The Imourkhssen Cu±Mo±Au±Ag porphyry-style mineralization is considered to be associated with the emplacement of the Askaoun granodiorite (ca. 558 Ma) and the Imourgane granite (ca. 551 Ma) that are coeval, respectively, with the 2nd and 3rd flare-ups reported in [15]. These two flare-ups correspond with the 2nd and 3rd magmatic pulses of the Ouarzazate SLIP (560 Ma and 550 Ma, respectively) [32]. The 3rd magmatic pulse could be also responsible for the occurrence of the Zgounder Ag-Hg epithermal ore deposit in the southwestern part of the studied area. In this regard, the potential relationship between the Imourkhssen porphyry and the Zgounder epithermal mineralization could be discussed.

Overall, this period could be correlated with regional events, highlighted by the transition from a transpressive to transtensive tectonic regime by the orogenic collapse [65]. In the framework of this extensional regime, leached hydrothermal fluids are inferred to have flowed along faults, developing the porphyry and epithermal deposits [15].

Consequently, the Ouarzazate SLIP could be potentially invoked as the metal source and hydrothermal energy that fueled the Late Ediacaran porphyry and epithermal hydrothermal and metallogenic activities in the central and eastern Anti-Atlas, namely, the Saghro domain of Morocco (see Section 5.4).

5.4. A Probable Late Ediacaran Porphyry-Epithermal Province in the Anti-Atlas

The post-collisional period in the Pan-African Anti-Atlas belt system involved the transition to a passive continental margin with a strong extensional tectonic regime and subsequent orogenic collapse [21,28]. In the framework of this extensional regime, intense metallogenic activity occurred, giving rise to numerous world-class precious metal epithermal deposits (Imiter and Zgounder), base metal porphyry, and SEDEX-type occurrences (Bou Madine; [28]) within outcrops formed mainly by highly silicic magmatism. This magmatism was speculated to be the Ouarzazate SLIP [28,30].

The consistency of the geological, geochemical, and metallogenic features of several precious and base metal occurrences occurring in the central and the eastern part of the Anti-Atlas are remarkable. This part of the Anti-Atlas chain delimited by the southern High Atlas fault (SAF) and the Anti-Atlas major fault (AAMF) was recently considered as a single terrane, referred to as the Saghro domain [30]. On the other hand, numerous ore deposits show a spatial and probably a temporal link with Late Ediacaran silicic magmatism of the Ouarzazate SLIP within the Saghro domain

In the framework of the extensional tectonic regime and the long-lived magmatic activity of the Ouarzazate SLIP [32,33], the authors of [15] proposed that Jbel Saghro constitutes a large mineralized provin6ce regarding pervasive hydrothermal activity and several metallogenic manifestations. In this paper, we propose that the Saghro domain should be considered as a Late Ediacaran porphyry-epithermal province englobing the entirety of porphyry and epithermal ore deposits linked to the post-orogenic collapse episode of the Pan-African orogen (Figure 21).

Figure 21. The emplacement of many ore porphyry and epithermal deposits within the Saghro domain, creating a Late Ediacaran porphyry epithermal province in the Anti-Atlas of Morocco [15]. Abbreviations: SAF: south Atlas fault, AAMF: Anti-Atlas major fault.

Figure 21. The emplacement of many ore porphyry and epithermal deposits within the Saghro domain, creating a Late Ediacaran porphyry epithermal province in the Anti-Atlas of Morocco [15]. Abbreviations: SAF: south Atlas fault, AAMF: Anti-Atlas major fault.

This system was powered by the injection of silicic magmatic pulses of the Ouarzazate SLIP. In three epochs, the incorporated juvenile sulfide-rich related subduction component of the melted magma allowed to the emplacement of fertile intrusions. These intrusions developed porphyry and epithermal mineralizations under a single porphyry–epithermal system. This system, with the associated SLIP magmatism, occurred during the latest post-collisional episodes of the Pan-Africain orogeny, corresponding with the metacratonic evolution of the northern edge of the West African craton (WAC) [90,91].

5.5. Similarities with Porphyry and Epithermal Ore Deposits in the World

The mineralization style of the porphyry and epithermal ore deposits and related magmatic activity occurring in the Saghro domain are widely recognized in several ore deposits around the world.

Before debating the porphyry–epithermal relationship, we can discuss the multi-pulse feature of the hydrothermal-magmatic activity responsible for the huge metallogenic activity during the Late Ediacaran times. Indeed, this multi-pulse character is broadly recognized in the development of several ore deposits, such as the Cu-Pb-Zn polymetallic deposit in Jiangxi Province. The latter is considered to be tied to three main magmatic-hydrothermal events (ca. Middle-Late Triassic, Late Jurassic, and Early Cretaceous) that are responsible for the metallogenic activity in the North Wuyi area of China [92].

In Jiangxi province, East China, the porphyry Cu-Au-Mo mineralizations and the Ag-Pb-Zn epithermal occurrences are related to five magmatic phases recognized in the Dexing area [75]. Based on the geochronogical and geochemical features of both mineralization styles, those authors reasonably assumed a link between the Dexing Cu-Au-Mo porphyry and Ag-Pb-Zn epithermal ore deposits in Jiangxi province.

The connection between the porphyry and epithermal deposits envisaged in the Saghro domain is observed in several ore deposits worldwide. Indeed, numerous epithermal ore deposits are underlain by porphyry-type mineralization, often rooted in their advanced argillic alteration lithocaps [1,93]. In China, several porphyry and epithermal deposits are suggested to be genetically related. Namely, the Yinshan Ag-Pb-Zn epithermal and Cu-Au porphyry ore deposits [94].

Moreover, the epithermal deposits can also be grounded within the serecitic alteration zone (e.g., the Far Southeast-Lepanto (FSEL) Cu-Au porphyry and epithermal deposits; [95]). In this example, the examination of fluid inclusions and δO and δD compositions led the researchers to conclude that gradational alteration patterns from advanced argillic alteration, through phyllic and K-silicate alterations, could be used to outline the spatial evolution of a single hydrothermal fluid during the formation of the FSEL porphyry and the epithermal district in the Philippines [95].

On the other hand, discussing the relationship between porphyry and epithermal ore deposits involves understanding the metal source [1]. For this reason, the authors of [95] assumed a common magmatic metal source for the entire FSEL porphyry-epithermal mineralization stages based on similar metal associations. Therefore, the identical magmatic fluid sources for both porphyry and epithermal systems is the best evidence for their genetic connection.

In the Baguio mineral district, the Philippines, two (I and II) porphyry vein stages are superimposed by four (III to V) paragenetic stages of the Acupan epithermal mineralizations [96]. Fluid-inclusion studies revealed that the porphyry vein stages were sourced from hot and hypersaline magmatic fluids exsolved during the crystallization of the subvolcanic porphyry dacite, while the co-existing magmatic vapor generated gold and silver epithermal mineralizations alongside gang and alteration patterns. This mineralization style was also guided by structures associated with the emplacement of the Balatoc diatreme [96].

A further example in the Apuseni Mountains, Romania, is reported in [97]. Those authors demonstrated using 3D structural measurements that there is a spatial link between the Bolcana Cu-porphyry and three epithermal deposits (e.g., Troita, Trestia, and Magura). This study was based on studding in 3D the spatial dispersion of metal contents around the Bolcana Cu-porphyry, revealing a specific distribution that could not result from a telescoped system. Thus, a strong relationship between porphyry copper and epithermal ore deposits occurs within the Apuseni Mountains.

5.6. Spatial Correlation with the Avalon Epithermal Ore Deposits

During the Late Ediacaran period, as Gondwana was nearing its final amalgamation, the West African craton (WAC) was surrounded by Pan-African terranes (Figure 22), which included island arcs or continental active margins. In this context, the WAC assumed the role of a passive margin amidst these geological features ([91] and references therein). During the Paleozoic era, terranes adjacent to the northwestern edge of Gondwana separated, resulting in the formation of the Rheic Ocean [98]. Hence, specific peri-Gondwanan terranes exhibit significant similarities in age, tectonic evolution, metallogenic history, and facies progression to the Pan-African belts found in the West African craton, including the Anti-Atlas. Here, we mainly focus on the metallogenic aspect as a tool for global correlation.

Indeed, most of the epithermal alterations and related mineralizations identified in the Avalon zone occurring from 590 to 550 Ma are also associated with potential buried porphyry deposits [100]. In this regard, the Late Neoproterozoic epithermal mineralization of the Saghro porphyry-epithermal province portrays a link with the west Avalon zone’s epithermal deposits.

Indeed, the Hickey’s Pond, Big Easy, Long Harbour, Hope Brook, and Heritage epithermal deposits occur in the Newfoundland area of the west Avalon zone. The Hickey’s Pond high-sulfidation deposits [101] have an age of 586 ± 3 Ma from the advanced argillic alteration [102]. A reinterpretation of the age from the host rocks provides a younger age of 572.5 ± 1.5 Ma [103]. Further studies of the Hope Brook high-sulfidation deposits bracketed the age of the alteration and the mineralization between 578 and 574 Ma [104]. The Big Easy epithermal deposit has a Late Neoproterozoic age (ca. 573 Ma; [103]), while the Long Harbour prospect, a mineralized rhyolite, constrains the age of this low epithermal deposit at 566.5 ± 1.9 Ma and has been used to indicate its alkaline affinity and potential relationship with late arc-extension [103]

On the other hand, the correlation between the WAC edge and the boundary of North America is currently debated. Based on geochemical and geochronological data, the authors of [30] proposed potential correlations between the magmatic rocks of the Ouarzazate Group outcropping in the Ifni inlier and the magmatic rocks of west Avalonia, including the Newfoundland area. The authors of [105] interpreted the Late Ediacaran magmatism in the El Jadida region as an example of a Moroccan peri-Gondwanan (Avalonian?) remnant, while the authors of [106] described many fossils found in the Anti-Atlas of Morocco (e.g., Aspidella) that are ubiquitous in the Avalon zone. These fossils point to the Ediacaran period and underscore a similar deposit style.

Here, we suggest a spatial link between the northern boundary of the West African craton (WAC), namely the Saghro domain, and the west Avalon zone during the Late Ediacaran times.

6. Conclusions

This study allows us to draw several conclusions, which we summarize below:

(1) We support the hypothesis of porphyry-type mineralization for the Imourkhssen deposit (central Anti-Atlas, Morocco), which was previously suggested in [32]. We argue this based on the following points: (i) the geochemical nature of the host rocks and multi-phase magmatic (Assarag, Amassine, and Ougougane suites) and hydrothermal activities, (ii) the style and the zonation of hydrothermal alteration and mineralization, (iii) the mineral assemblage and paragenetic sequence, and (iv) the post-collisional geodynamic setting of the host rocks.

(2) The model envisaged in this study for the Imourkhssen Cu±Mo±Au±Ag mineralization could be related to the 2nd and the 3rd flare-ups reported in [15], which are coeval with the 2nd and the 3rd magmatic pulses of the Ouarzazate SLIP, as evidenced in [33].

(3) The ore genesis potentially involves the Zaghar mafic dykes during the magma evolution, which is corroborated by their co-mingling textures.

(4) The concordia and ²⁰⁶Pb/²³⁸U ages and averages of the barren Imourkhssen and the ore-bearing granite from the TV area allow us to constrain the age of the Imourkhssen intrusion at 558 ± 1 Ma.

(5) The ore-bearing granite is newly identified as the “Imourgane granite.” The concordia age of 550 ± 2 Ma indicates that it belongs to the Ougougane suite, and this allows us to constrain the age of the porphyry–epithermal system in the OSS beneath the 2nd and 3rd magmatic pulses of the Ouarzazate SLIP.

(6) Several ore deposits in the whole Anti-Atlas seem to belong to a Late Ediacaran porphyry–epithermal system linked to the emplacement of a multi-pulse continental silicic large igneous province, namely, the Ouarzazate SLIP (580–539 Ma). This SLIP was generated during the post-collisional period of the Pan-African orogen.

(7) The average ages of the epithermal ore deposits of the west Avalon zone and the porphyry-epithermal province entail their potential spatial link during the Late Neoproterozoic times, corresponding with the metacratonic evolution of the northern boundary of the West African craton.