Geochemical Characteristics and Zircon U-Pb Geochronology of Diabase in the Jinchanghe Mining Area, Western Yunnan, SW China: Implications for Tectonic and Magmatic Evolution of the Baoshan Block

Abstract

The Jinchanghe Fe-Cu-Pb-Zn polymetallic deposit is located in the northern Baoshan block in the Sanjiang metallogenic belt, southwestern China, and is one of the major large-scale Pb-Zn polymetallic deposits. This region is characterized by numerous diabase intrusions; however, research work is limited. This study elucidated systematic geochemistry and chronology of the diabase closely associated with orebodies in Jinchanghe to provide constraints for magma evolution. The results indicated that the Jinchanghe diabase was enriched in CaO, MgO, and Al₂O₃ and depleted in TiO₂ and P₂O₅. Large ion lithophile elements were depleted, while for high field strength elements, the ratio of LREEs but depleted in HREEs. The zircon U-Pb dating results suggested that the diabase age could be divided into two stages, indicating the occurrence of two-stage tectonic-magmatic events in the Late Triassic and Early Cretaceous. The results also suggested that the metallogenic age of the Jinchanghe deposit is the Early Cretaceous. Moreover, the age was closely related to the collision after the closure of the mid-Tethys Ocean in the Early Cretaceous. Therefore, the results of this study provide new evidence for the tectonic-magmatic evolution and mineralization of the Baoshan block.

1. Introduction

The Jinchanghe Fe-Cu-Pb-Zn polymetallic deposit is located in the northern Baoshan block and is part of the “Sanjiang” (i.e., Jinsha, Lancang, and Nujiang River) polymetallic metallogenic belt in southwest China. It is also a typical representative Pb-Zn polymetallic deposit in the Baoshan block. The Yunnan Gold Mining Group Co., Ltd. has conducted a series of explorations in the Jinchanghe mining area since 2004. Previous studies on mineralogical characteristics and alteration zoning have indicated that the ore body is characterized by Pb, Zn-Cu, and Cu-Fe vertical zoning and Fe, Cu-Pb, and Zn-Cu horizontal zoning [1,2]. Additionally, the mineralization age has been assigned to the Early Cretaceous [3]. Studies on the alteration zoning of the deposit have speculated that the Jinchanghe Fe-Cu-Pb-Zn polymetallic deposit is skarn-type [4]. In this type of mineral deposit genesis, there is a significant regional negative gravity anomaly according to gravity anomaly data, which may have a close genetic relationship with lead-zinc polymetallic deposits [5]. Due to the low degree of research in the mining area, so far the mineralization-related intermediate-acidic rock mass is not revealed. The surface of the mining area can be seen in diabase island-lenticular distribution. After detailed observation under a microscope, the main components of diabase are determined as pyroxene and basic feldspar. In addition, the diabase intrusion in the mining area is generally in close contact with the ore bodies. The exposed area is approximately 0.11–0.39 km² with ecliptic alterations. However, systematic research on the diabase in the mining area is limited.

Therefore, this study conducted a systematic geochemical analysis of the diabase in the Jinchanghe mining area and determined its zircon U-Pb age. Additionally, its tectonic setting and material source area were determined, and the relationship between the Fe-Cu-Pb-Zn polymetallic deposit and the diabase intrusion was analyzed. The results of this study provide a baseline reference for further understanding of the genesis of deposits in the study region.

2. Regional Geological Background

The Baoshan block is an important part of the Tethys in western Yunnan [6,7,8]. It is located in the middle of the Tibetan-Yunnan-Thai-Ma middle plate and extends southward from the border to connect with Shan State and subsequently form the SIBMASU terrane [9,10]. The eastern side is bounded by the Kejie-Nandinghe fault, which is adjacent to the Changning-Menglian belt. The western side is connected with the Tengchong block and is separated by the Lushui-Luxi-Ruili fault. The merging of the Lancangjiang and Nujiang faults resulted in the extinction of the northern part of the Baoshan block in the Bijiang area (Figure 1). Under the influence of regional tectonic evolution, this area has mainly experienced two long geological evolution processes: Cambrian to Early Permian Proto-Tethys and Paleo-Tethys stable platform and platform basin stage, and Late Early Permian to Triassic Paleo-Tethys subduction collision stage [11].

The main faults in the study area are Lancangjiang and Nujiang, while the secondary faults are Kejie and Wayao-Yunxian. The regional fault structure line is affected by the main faults and exists in the NE, NW, SN, and EW directions [5]. The Baoshan-Shidian complex anticline, which is north of Wafang and south of Mengxing, is the main fold in the region. Its control boundaries are all faults, and the overall extension is close to the SN direction.

Additionally, several secondary folds and main veins are visible at the secondary fold axis or the anticline-syncline transition. Strata ranging from the Paleozoic to the Cenozoic are exposed, and the Gongyangmenghe group (Z-Єgy) in the Sinian-Cambrian represents the oldest stratum. Among these, the Early Paleozoic stratum indicates the widest range of exposure as well as the most complete development, characterized by the presence of shallow-semi-deep marine carbonates, clastic rocks, siliceous rocks, and shale deposits [12]. Most carbonates and clastic rocks have metamorphosed into marble, marbled limestone, and silty slate [13].

Magmatic rocks are widely exposed in the study area and developed from the Precambrian to the Mesozoic. The Precambrian is characterized by Laojiezi and Luxi granites with Rb-Sr isochron ages of 687 and 645 Ma, respectively [1]. Pinghe granite from the Early Paleozoic is the most widely distributed granite body in the Baoshan block, and its zircon U-Pb age range is 466–502 Ma [14,15,16,17]. The Late Paleozoic magmatic rocks include Muchang alkaline granite, Daxueshan ultrabasic rock mass, and Dashan rock mass [11]. The Mesozoic and Cenozoic magmatic rocks are represented by the Zhibenshan granite body in the northern Baoshan block, two-mica granites in the Yunlong metallogenic belt [18], Shuangmaidi rock mass [18], and monzonitic granite of the Longling-Luxi area [18,19]. In addition, numerous diabases with rock walls and veins are produced in the area.

3. Geological Features of Jinchanghe Deposit and Petrographic Characteristics of the Diabase

The Jinchanghe Fe-Cu-Pb-Zn polymetallic deposit is located in the northern Baoshan block at the intersection of the Muguashu-Zhushiqin (SN direction) and Muguashu-Ashizhai (NW direction) faults (Figure 2). The faults controlled the development of the derivative secondary structure of the deposit, while the fractures formed a herringbone. The Cambrian, Ordovician, Silurian, Devonian, and Quaternary strata are predominantly exposed in the mining area. Metamorphic carbonate rocks in the middle section of the Upper Cambrian Formation (Є₃h²) constitute the main ore-bearing horizon of the deposit.

The fault structures in the mining area are largely present in the NW, NE, and SN directions. Among these, faults F₂ and F₁₀, with evident ore-control characteristics, are the main ore-controlling structures. The F₂ fault declines to the SW with a dip angle of 74°. Additionally, its structural fracture zones are well developed in the northwest segment and accompanied by diabase intrusion. The F₁₀ fault declines to the SE with a dip angle of 70° and indicates characteristics of torsional normal fault activity. Jinchanghe uplift is the main fold in this region. The stress concentration acts on the axial part of the fold to result in the formation of tensile cracks, which provide favorable ore-bearing space for the deposit.

Magmatic rocks in the mining area are largely island-like with a lenticular distribution of diabase and an exposed area ranging from 0.11 to 0.39 km². The lenticular diabase intrusions are mainly distributed in the tunnel (Figure 3a). The rock is gray-green with idiomorphic or hypidiomorphic granular and block structures (Figure 3b). The diabase indicated residual diabasic texture under the microscope (Figure 3d), and its main minerals were plagioclase (30 wt%), pyroxene (20 wt%), and minor minerals such as amphibole, biotite, and quartz. Among these, plagioclase was partially altered into albite and zoisite, while pyroxene was partially altered to amphibole (Figure 3c,d).

4. Sample and Analysis Method

4.1. Sample Collection

In order to systematically study the geochemical characteristics and chronology of the Jinchanghe diabase, eighteen representative samples were collected from typical boreholes in different ore sections of the Jinchanghe mining area. The samples were taken from ZK4k-7x drill holes, ZK4k-13x drill holes, ZK4k-9xx drill holes, ZK2k-8xs1 drill holes, ZK8-4 drill holes, and ZK3k-11x (sample information is shown in

Table 1. Sample statistics of diabase in the Jinchanghe Fe-Cu-Pb-Zn deposit.

Sample Number	Rock Type	Sampling Location
JCH6-01	Gray-green diabase	ZK4k-7x drill holes, depth of 25 m
JCH6-15	Gray-green diabase	ZK4k-13x drill holes, depth of 36.95 m
JCH6-27	Gray-green diabase	ZK4k-9xx drill holes, depth of 45 m
JCH6-36	Gray-green diabase	ZK4k-13s drill holes, depth of 30 m
JCH6-39	Gray-green diabase	ZK2k-8xs1 drill holes, depth of 28 m
JCH7-05-1	Gray-green diabase	ZK8-4 drill holes, depth of 1470 m
JCH7-05-2	Gray-green diabase	ZK8-4 drill holes, depth of 1472 m
JCH7-05-4	Gray-green diabase	ZK8-4 drill holes, depth of 1473 m
JCH7-07	Gray-green diabase	ZK8-4 drill holes, depth of 491 m
JCH7-13	Gray-green diabase	Main roadway 150 m in the middle section of 1660
JCH8-4	Gray-green diabase	ZK2k-8xs1 drill holes, depth of 28 m
JCH8-27	Gray-green diabase	ZK2k-8xs1 drill holes, depth of 46 m
JCH8-29	Gray-green diabase	ZK2k-8xs1 drill holes, depth of 47 m
JCH8-37	Gray-green diabase	ZK2k-8xs1 drill holes, depth of 48 m
JCH8-39	Gray-green diabase	ZK3k-11x drill holes, depth of 45 m
JCH8-40	Gray-green diabase	ZK3k-11x drill holes, depth of 29 m
JCH8-41	Gray-green diabase	ZK3k-11x drill holes, depth of 32.5 m
JCH8-50	Gray-green diabase	ZK3k-11x drill holes, depth of 34 m

). The collected samples had no cracks and were relatively fresh, so they were well represented. Samples JCH6-01 diabase (from ZK4k-7x drill holes, depth of 25 m) and JCH7-07 diabase (from ZK8-4 drill holes, depth of 491 m) were used for zircon dating.

4.2. Analytical Method

4.2.1. Zircon U-Pb Ages and Hf Isotopic Composition

Zircons were separated by conventional heavy liquid and magnetic techniques before the separations were purified by handpicking under a binocular microscope. The resulting zircons were mounted in epoxy resin, polished, gold-coated, and then photographed under transmitted and reflected light. Zircon internal textures were examined through cathodoluminescence (CL) imaging prior to U-Pb isotopic analysis. Zircon U-Pb dating, and trace element analysis of zircon were simultaneously conducted by LA-ICP-MS at the Wuhan SampleSolution Analytical Technology Co., Ltd., Wuhan, China. Detailed operating conditions for the laser ablation system and the ICP-MS instrument and data reduction were the same as those described by Zong et al. (2017) [20]. Laser sampling was performed using a GeolasPro laser ablation system that consists of a COMPexPro 102 ArF excimer laser and a MicroLas optical system. Zircon 91500 and glass NIST610 were used as external standards for U-Pb dating and trace element calibration, respectively. A piece of Excel-based software ICPMSDataCal was used to perform off-line selection and integration of background and analyzed signals, time-drift correction, and quantitative calibration for trace element analysis and U-Pb dating [21].

Zircon Lu-Hf isotope analysis was completed at the State Key Laboratory of Geological Processes and Mineral Resources (GPMR) of China University of Geosciences (Wuhan), and the experiment was completed using the coherent 193 nm excimer laser ablation system (GeoLasPro HD) and Neptune Plus multi-receiver plasma mass spectrometry. The diameter of the laser ablation spot beam was 44 μm, and the detailed parameters of the instrument are shown in Liu et al. (2010b) [22]. The sample tested used 91,500 and the international zircon standard GJ-1 as the standard at the same time, of which the weighted average of ¹⁷⁶Hf/¹⁷⁷Hf tested for 91500 was 0.282308 ± 12 (2σ), and the weighted average of ¹⁷⁶Hf/¹⁷⁷Hf test of GJ-1 was 0.282013 (2σ). The Zircon Hf isotope analysis point was on and near the Zircon U-Pb isotope age analysis point with the same structure. The data processing was completed using the software ICPMSDataCal 12.0 for the experimental process and data processing method.

4.2.2. Whole-Rock Geochemistry Analysis

Samples of major and trace element geochemistry were collected from Jinchanghe diabase. Whole-rock major and trace element analyses were conducted at the ALS minerals laboratory, Guangzhou, China. Further, major oxides were analyzed by X-ray fluorescence spectroscopy (XRF), with analytical uncertainties of <0.5% used. Trace element concentrations were determined by Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES).

5. Results

5.1. Geochemical Characteristics

The analysis of the main trace elements in Jinchanghe diabase (

Table 2. Major element oxides (wt%) and trace element (ppm) of diabase in the Jinchanghe Fe-Cu-Pb-Zn deposit.

Sample Number	JCH6-01	JCH6-15	JCH6-27	JCH6-36	JCH6-39	JCH7-05-2	JCH7-05-1	JCH7-05-4	JCH8-4	JCH8-27	JCH8-29	JCH8-37	JCH8-39	JCH8-40	JCH8-41	JCH8-50	JCH7-13	JCH7-07
SiO2	45.63	48.43	43.98	42.66	43.4	47.01	45.45	46.82	44	43.12	44.78	42.16	43.1	44.26	42.02	47.12	43.61	44.31
Al2O3	15.08	14.88	13.18	11.91	13.22	14.27	17.14	14.97	11.29	13.04	15.09	10.96	12.58	13.25	13.94	14.17	12.36	13.22
TiO2	2.4	1.71	2.26	2.15	1.98	2.03	1.15	1.67	1.85	2.25	2.28	2.27	1.89	2.17	2.74	1.23	1.08	2.07
FeOT	12.37	11.78	14.16	13.85	13.09	11.12	11.18	12.48	13.82	14.22	12.42	15.65	12.98	14.44	14.95	10.74	10.92	13.58
MgO	6.75	6.59	10.43	11.35	9.13	6.8	5.84	7.54	12.5	10.3	8.11	12.5	9.71	11.15	9.09	12.80	15.15	9.59
CaO	11.96	9.63	8.07	11.41	8.36	13.13	15	11.7	10.9	9.04	8.66	10.8	8.94	8.21	11.4	5.21	8.07	9.62
Na2O	2.27	2.98	2.59	1.41	2.5	2.02	1.46	2.2	1.5	2.5	3.61	1.02	2.39	2.24	1.44	2.42	1.62	2.73
K2O	0.446	0.079	0.418	0.367	0.934	0.25	0.16	0.18	0.44	0.49	0.43	0.46	1.01	0.47	0.51	1.58	0.72	0.31
MnO	0.43	0.297	0.203	0.176	0.204	0.18	0.19	0.2	0.21	0.22	0.17	0.24	0.21	0.31	0.52	0.13	0.15	0.26
P2O5	0.204	0.202	0.319	0.205	0.293	0.26	0.11	0.15	0.23	0.28	0.36	0.18	0.28	0.24	0.2	0.11	0.1	0.31
LOI	2.45	3.38	4.37	4.51	6.87	2.41	2.39	2.57	3.86	4.79	4.43	3.98	7.65	3.79	3.08	4.56	6.75	4.72
Total	99.99	99.96	99.98	100	99.98	99.47	100.07	100.48	100.6	100.25	100.34	100.22	100.74	100.53	99.89	100.07	100.53	100.72
Rb	19.7	1.34	11.4	14.1	67.3	9.81	7.4	8	6	16.2	13.9	22.5	78.9	21.4	31.3	36.7	14.3	4.6
Ba	156	29.4	228	250	194	29.6	18.2	21	362	227	285	207	154.5	232	133.5	349	119	257
Sr	830	397	265	464	263	469	668	416	375	373	547	377	262	298	699	196	176	332
Nb	25.4	28.4	37.2	28.7	37.5	12.6	4.9	7.2	25.5	32	41.9	21.6	31.3	28.1	25	7.8	6.6	36.7
Th	2.5	3.54	3.15	2.8	3.53	1.59	0.93	1.28	2.9	3.09	3.23	2.13	2.97	2.91	2.86	2.06	1.84	3.31
Pb	7.84	4	3.71	8.12	6.77	10.2	17.4	7.1	7.1	5.2	4.5	5.3	5.4	5.5	6.9	1.6	1.1	2.7
Zn	122	124	153	127	136	85.8	63	82	123	123	99	126	120	144	141	71	77	121
Cu	61.2	32.8	72	124	81.5	106	42.6	27.3	102	88.8	44.9	84.4	74.6	116.5	27.6	149	143.5	76.2
Ni	59.1	58.2	260	260	224	79.3	63.2	88.3	367	268	161	319	261	283	180.5	394	553	234
Co	44.3	38.6	69.5	74.5	61.8	92.9	25.6	38.7	69.5	64.3	48.7	74.7	58.3	59.3	65.3	60.4	59.1	57.3
V	275	257	295	353	242	386	354	343	288	318	225	423	265	347	483	313	270	276
Cr	74.1	153	439	514	390	157	137	188	700	466	285	578	458	551	270	934	1287	428
U	0.47	0.68	0.7	0.6	0.67	0.41	0.28	0.3	0.68	0.76	0.80	0.57	0.73	0.78	0.67	0.5	0.43	0.86
Ta	1.83	1.6	2.49	2	2.57	0.66	0.34	0.43	1.80	2.19	2.88	1.58	2.26	1.99	1.88	0.5	0.42	2.64
Zr	77.4	49.1	96.4	87.90	74.4	26.4	72	95	127	151	158	118	140	145	131	89	74	158
Hf	2.68	1.75	3.41	3.12	2.58	1.67	2.1	2.8	3.7	4.3	4.3	3.8	3.8	4.3	3.7	2.7	2.2	4.4
La	17.6	19.7	24.1	18.5	25	8.16	6.3	6.9	19.7	23.3	26.5	16.5	23.5	21	19.5	9.7	8.5	26.2
Ce	33.5	38.1	47.7	32.9	49.2	19.8	16.3	17.9	40.1	47.8	54.8	34.2	46.5	43.1	38.8	20.4	17.8	53.4
Pr	4.67	4.76	5.66	4.76	5.79	2.75	2.05	2.42	4.99	6	7.06	4.35	5.82	5.49	4.95	2.72	2.35	6.56
Nd	19.6	17.5	28.1	20.9	25.3	14.3	9.4	11.4	20.1	24.3	28.1	18.7	23.1	22.1	20.4	12.4	10.5	25.9
Sm	4.18	4.41	5.57	4.88	5.76	4.17	3.02	3.39	4.86	5.63	6.51	4.56	5.19	5.41	5.05	3.68	3.11	6.23
Eu	1.81	1.52	1.66	1.9	1.72	1.13	1.6	1.13	1.73	1.94	2.08	1.64	1.61	1.79	1.57	1.20	1.12	1.79
Gd	4.26	4.25	5.24	4.4	4.99	4.97	3.79	4.51	4.66	5.65	6.29	4.87	4.83	5.40	4.74	4.75	3.77	5.89
Tb	0.73	0.87	0.93	0.82	0.84	0.88	0.64	0.74	0.68	0.78	0.9	0.68	0.72	0.79	0.74	0.79	0.64	0.86
Dy	4.06	4.78	4.16	4.05	4.36	5.95	4.12	4.73	3.79	4.38	4.87	3.73	3.68	4.41	3.97	4.97	4.09	4.48
Ho	0.65	0.95	0.8	0.76	0.74	1.17	0.93	1	0.67	0.77	0.9	0.66	0.67	0.80	0.68	1.05	0.88	0.79
Er	1.74	2.67	1.87	1.77	1.82	3.4	2.64	2.88	1.63	1.85	2.11	1.63	1.68	1.92	1.7	2.99	2.46	1.96
Tm	0.24	0.41	0.28	0.25	0.25	0.46	0.41	0.42	0.21	0.24	0.27	0.22	0.22	0.25	0.22	0.42	0.37	0.26
Yb	1.24	2.25	1.57	1.44	1.5	2.86	2.77	2.58	1.2	1.41	1.68	1.23	1.25	1.45	1.31	2.61	2.28	1.52
Lu	0.16	0.29	0.18	0.17	0.16	0.39	0.42	0.36	0.17	0.2	0.25	0.18	0.19	0.2	0.18	0.41	0.33	0.22
Y	18.1	25.1	18.1	18.4	18.9	29	23.7	25.1	16.1	18.7	21.8	16.4	16.9	19.5	17.1	26.6	22.5	19.7
ΣREE	94.43	102.45	127.83	97.49	127.43	70.4	54.39	60.36	104.49	124.25	142.32	93.15	118.96	114.11	103.81	68.09	58.2	136.06
LREE	81.36	85.99	112.79	83.84	112.77	50.31	38.67	43.14	91.48	108.97	125.05	79.95	105.72	98.89	90.27	50.1	43.38	120.08
HREE	13.07	16.46	15.04	13.65	14.66	20.09	15.72	17.22	13.01	15.28	17.27	13.2	13.24	15.22	13.54	17.99	14.82	15.98
LREE/HREE	6.23	5.22	7.5	6.14	7.69	2.50	2.46	2.51	7.03	7.13	7.24	6.06	7.98	6.5	6.67	2.78	2.93	7.51
(La/Yb)N	10.18	6.28	11.01	9.22	11.95	2.05	1.63	1.92	11.78	11.85	11.31	9.62	13.49	10.39	10.68	2.67	2.67	12.36
δEu	1.3	1.06	0.92	1.23	0.96	0.76	1.45	0.88	1.1	1.04	0.98	1.06	0.97	1	0.97	0.88	1	0.89

Note: LOI = loss on ignition, total iron reported as FeO^T.

) indicated that the SiO₂ content ranged between 42.02 wt% and 48.43 wt%, with an average of 44.54 wt% obtained, and the Al₂O₃ content ranged between 10.96 wt% and 17.14 wt%, with an average of 13.59 wt% obtained. The TiO₂ content ranged between 1.08 wt% and 2.74 wt%, with an average of 1.95 wt% obtained. Additionally, the K₂O content ranged between 0.079 wt% and 1.58 wt%, with an average of 0.51 wt% obtained, while that of Na₂O ranged between 1.02 wt% and 3.61 wt%, with an average of 2.16 wt% obtained. The Na₂O content was higher than that of K₂O. Moreover, the results indicated a higher alkali content, and the total alkali (Na₂O+K₂O) content ranged between 1.48 wt% and 4.04 wt%, with an average of 2.68 wt% obtained. The rocks were relatively enriched in Na and depleted in K. Furthermore, the Na₂O/K₂O ratio ranged from 1.53 to 37.72. The P₂O₅ content ranged from 0.10 wt% to 0.36 wt%, with an average of 0.22 wt% obtained. The analysis of geochemical characteristics suggested that the Jinchanghe diabase is enriched in CaO, MgO, and Al₂O₃ and depleted in TiO₂ and P₂O₅.

Eighteen samples were plotted on the Gabbro region in the intrusive rocks TAS diagram (Figure 4a). Among these, ten samples were assigned to the alkaline area, while the remaining samples were assigned to the sub-alkaline region. Additionally, the evolution of alkaline to sub-alkaline indicated that the basic magma experienced moderate differentiation during diagenesis of the Jinchanghe diabase. The data for the SiO₂-K₂O diagram (Figure 4b) were plotted on the calc-alkaline and low-potassium series. The Mg^# values ranged between 48.22 and 71.21, with an average of 56.42 obtained, and were lower than that of the original magma [23]. The Hark diagram for the main elements indicated (Figure 5) that CaO, Al₂O₃, and MgO were negatively correlated, thus suggesting plagioclase crystallization differentiation. However, P₂O₅, FeO^T, and MgO indicated positive correlations, which suggested that the basic magma was characterized by apatite and Fe oxide separation and crystallization during the formation process.

The trace element analysis results for Jinchanghe diabase are presented in Table 1. The total quantity of rare earth elements (∑REE) ranged from 54.39 ppm to142.32 ppm, with an average of 99.90 ppm obtained. The ratio of quantities of light rare earth elements (LREE) and heavy rare earth elements (HREE) ranged between 2.46 and 7.98, with an average of 5.67 obtained. The (La/Yb)_N values ranged between 1.63 and 13.49, thus indicating evident fractionation of the LREEs and HREEs. The δEu values ranged from 0.76 to 1.45, with an average of 1.02 obtained. The REE patterns exhibited LREE enrichment and indicated no obvious plagioclase crystallization in the original magma (Figure 6a).

Large ion lithophile elements, such as Ba, K, and Sr, were depleted in the primitive mantle, as indicated by the standardized spider diagram of trace elements (Figure 6b). Additionally, K was strongly depleted, while high field strength elements (HFSE), such as Th, Nd, and Hf, were enriched. The correlation diagram between MgO and the trace elements (Cr, Nb, Ni, Co, and V) (Figure 7) indicated positive correlations. Additionally, decreases in Cr and Ni indicated the occurrence of olivine and clinopyroxene crystallization differentiation in the basic magma.

In Table 2, 10.47 wt% and 15.65 wt%, with an average of 12.99 wt% obtained and was higher than that of the continental crust (6.7 wt%). The Cu content ranged from 27.3 ppm to 149.0 ppm, with an average of 80.83 ppm obtained, and was higher than the Cu content of the continental crust (27 ppm). The Pb content ranged from 1.1 ppm to 17.4 ppm, with an average of 6.14 ppm obtained, and was less than its content in the continental crust (11 ppm). The Zn content ranged between 63 ppm and 153 ppm, with an average of 113.21 ppm obtained, and was higher than the Zn content of the continental crust (72 ppm) [21]. Therefore, Fe, Cu, and Zn indicated high geochemical background values, thus suggesting that the diabase could be a source of ore-forming materials for the Jinchanghe Fe-Cu-Pb-Zn polymetallic deposit.

5.2. Zircon U-Pb Ages

In this study, twenty-four zircons were obtained from two diabase samples (JCH6-01, JCH7-07) for conducting the dating analysis. These included nineteen zircon samples from JCH6-01 and five from JCH7-07. Each zirconium was measured at one point. The analysis results are presented in

Table 3. LA-ICP-MS U-Pb data for zircon from diabase in the Jinchanghe Fe-Cu-Pb-Zn deposit.

Analysis	Pb	Th	U	Th/U	207Pb/206Pb	1σ	207Pb/235U	1σ	207Pb/235U	1σ	207Pb/235U	1σ	206Pb/238U	1σ	208Pb/232Th	1σ
	×10−6										Age (Ma)		Age (Ma)		Age (Ma)
JCH6-01
JCH6-01-01	297.7	3305.0	2794.3	1.18	0.0488	0.0021	0.2373	0.0105	0.0350	0.0006	216	9	222	4	213	6
JCH6-01-02	458.0	4455.0	4413.7	1.01	0.0567	0.0019	0.2879	0.0093	0.0368	0.0005	257	7	233	3	234	6
JCH6-01-03	377.0	3412.5	4933.7	0.69	0.0507	0.0019	0.2443	0.0097	0.0347	0.0004	222	8	220	3	216	5
JCH6-01-04	334.2	271.3	3749.7	0.07	0.0575	0.0016	0.6321	0.0177	0.0790	0.0008	497	11	490	5	626	27
JCH6-01-05	390.9	492.0	4618.4	0.11	0.0554	0.0015	0.5537	0.0158	0.0720	0.0009	447	10	448	6	469	15
JCH6-01-09	273.2	2517.3	2843.8	0.89	0.0503	0.0045	0.2302	0.0201	0.0332	0.0005	210	17	211	3	211	3
JCH6-01-13	96.9	473.6	649.6	0.73	0.0723	0.0127	0.3197	0.0557	0.0321	0.0008	282	43	203	5	195	4
JCH6-01-14	54.3	476.5	627.7	0.76	0.0533	0.0044	0.2435	0.0178	0.0344	0.0007	221	15	218	4	217	8
JCH6-01-15	311.7	2778.8	4044.8	0.69	0.0503	0.0019	0.2355	0.0092	0.0337	0.0005	215	8	213	3	209	6
JCH6-01-17	68.8	420.0	758.4	0.55	0.0593	0.0052	0.3100	0.0264	0.0379	0.0007	274	20	240	4	236	3
JCH6-01-20	379.8	722.1	1062.7	0.68	0.0510	0.0054	0.1443	0.0141	0.0205	0.0010	137	12	131	6	132	10
JCH6-01-21	442.6	726.3	1066.5	0.68	0.0487	0.0026	0.1364	0.0067	0.0203	0.0006	130	6	130	4	127	4
JCH6-01-22	150.1	194.4	453.1	0.43	0.0526	0.0040	0.1431	0.0100	0.0197	0.0008	136	9	126	5	118	7
JCH6-01-23	202.8	609.4	1035.9	0.59	0.0461	0.0071	0.1229	0.0183	0.0194	0.0007	118	17	124	5	126	5
JCH6-01-24	290.2	774.7	1272.7	0.61	0.0490	0.0055	0.1415	0.0146	0.0209	0.0011	134	13	134	7	121	11
JCH6-01-33	903.3	11,467.8	6957.6	1.65	0.0505	0.0016	0.2341	0.0071	0.0334	0.0004	214	6	212	2	202	5
JCH6-01-35	565.0	5640.9	6216.1	0.91	0.0760	0.0038	0.3597	0.0211	0.0329	0.0006	312	16	209	4	417	43
JCH6-01-38	44.7	282.2	614.3	0.46	0.0511	0.0040	0.2603	0.0198	0.0364	0.0008	235	16	230	5	277	18
JCH6-01-43	1081.9	11,318.5	7278.3	1.56	0.0461	0.0040	0.2188	0.0184	0.0345	0.0005	201	15	218	3	224	8
JCH7-07
JCH7-07-6	150	943	970	0.97	0.0499	0.0022	0.2347	0.0106	0.0339	0.0005	214	9	215	3	199	8
JCH7-07-16	89	548	585	0.94	0.0547	0.0026	0.2574	0.0118	0.0343	0.0005	233	10	217	3	331	185
JCH7-07-20	108	707	679	1.04	0.0542	0.0026	0.2493	0.0122	0.0333	0.0005	226	10	211	3	411	300
JCH7-07-25	165	1116	918	1.22	0.0538	0.0025	0.2503	0.0113	0.0336	0.0005	227	9	213	3	501	419
JCH7-07-28	71	478	411	1.16	0.0585	0.0031	0.2689	0.0134	0.0336	0.0007	242	11	213	4	560	494

. Figure 8 presents a zircon cathodoluminescence image with the zircon length ranging from 50 to 150 μm and a high aspect ratio (1 to 2.5). Eighteen zircons indicated a good degree of self-formation and were characterized by clear oscillating ring zones and obvious characteristics of magmatic zircon. The ²⁰⁶Pb/²³⁸U ages of 12 zircons from the JCH6-01 sample were found to be from 203 ± 5.0 to 240 ± 4.0 Ma. The age distribution was concentrated, and the 12 points were distributed on and around the consistent curve and indicated good concordance. Additionally, their weighted mean age was determined to be 216.9 ± 2.7 Ma (n = 12, MSWD = 1.5) (Figure 9a). The other five zircons from the JCH6-01 sample were largely semi-automorphic, the ring zones were not clear or undeveloped, and two zircons (6-01-6, 6-01-23) indicated spongy zircon secondary development. The structure showed characteristics of hydrothermal origin zircon. Their ²⁰⁶Pb/²³⁸U ages were found to range from 124 ± 5.0 to 144 ± 2.0 Ma, and the points were distributed on and near the harmonic curve. The weighted mean age was determined to be 130.5 ± 8.8 Ma (n = 5, MSWD = 0.34) (Figure 9a). This indicates that the Jinchanghe mining area experienced hydrothermal activity during this period and that the metallogenic time limit of the Jinchanghe Pb-Zn polymetallic deposit was the Early Cretaceous.

The ²⁰⁶Pb/²³⁸U ages of the five zircons from the JCH7-07 sample were found to range from 211 ± 3.2 to 217 ± 3.1 Ma, and the age distribution was concentrated. The five points were distributed on and around the consistent curve with good concordance, and the weighted mean age was found to be 213.9 ± 2.9 Ma (n = 5, MSWD = 0.51) (Figure 9b). Thus, the results indicate that the crystallization age of the diabase is 213.9 ± 2.9 Ma, and that the diabase is a product of the Late Triassic magmatism.

5.3. Zircon Hf Isotopes

This paper analyzed the Lu-Hf isotopes of two zircon samples. As part of the analysis, points were pierced by the laser beam spot, and 23 effective analysis points were finally obtained. The analysis data are shown in

Table 4. LA-ICP-MS zircon Lu-Hf isotopic data of Jinchanghe diabase.

Sample	176Yb/177Hf	176Lu/177Hf	176Hf/177Hf	2σ	(176Hf/177Hf)i	εHf(0)	εHf(t)	2σ	TDM (Ma)	TCDM (Ma)	f(Lu/Hf)
JCH6-01	0.034114	0.001293	0.282754	0.000010	0.282749	−0.7	4.0	0.3443	711	995	−0.96
JCH6-02	0.039244	0.001485	0.282708	0.000008	0.282702	−2.4	2.6	0.2960	781	1093	−0.96
JCH6-03	0.046999	0.001873	0.282768	0.000009	0.282760	−0.3	4.4	0.3121	702	970	−0.94
JCH6-05	0.049139	0.001974	0.282802	0.000016	0.282795	1.0	5.4	0.5734	654	898	−0.94
JCH6-06	0.051589	0.001941	0.282983	0.000011	0.282976	7.4	11.7	0.3955	391	493	−0.94
JCH6-07	0.069213	0.002488	0.283015	0.000016	0.283005	8.5	12.7	0.5566	350	428	−0.93
JCH6-08	0.054179	0.002054	0.283003	0.000014	0.282995	8.0	12.4	0.4848	363	448	−0.94
JCH6-09	0.080386	0.002730	0.282385	0.000009	0.282362	−13.8	−4.7	0.3204	1284	1718	−0.92
JCH6-10	0.080694	0.002587	0.282413	0.000010	0.282389	−12.8	−2.8	0.3571	1238	1630	−0.92
JCH6-11	0.050359	0.001779	0.282980	0.000012	0.282973	7.2	11.4	0.4270	394	504	−0.95
JCH6-15	0.059563	0.002607	0.282735	0.000011	0.282726	−1.4	2.4	0.3917	766	1071	−0.92
JCH6-17	0.054453	0.002054	0.282984	0.000014	0.282975	7.4	11.9	0.4885	391	489	−0.94
JCH6-18	0.068578	0.002523	0.282974	0.000018	0.282964	7.0	11.5	0.6198	410	514	−0.92
JCH6-19	0.058206	0.002147	0.283006	0.000016	0.282997	8.2	13.0	0.5720	359	429	−0.94
JCH6-04	0.09104	0.001154	0.282725	0.000009	0.282722	−1.8	1.4	0.3263	750	1104	−0.97
JCH6-12	0.024444	0.000857	0.282923	0.000012	0.282921	5.2	8.1	0.4088	465	665	−0.97
JCH6-13	0.060041	0.002276	0.282764	0.000012	0.282759	−0.4	2.3	0.4413	716	1034	−0.93
JCH6-16	0.056681	0.002147	0.282984	0.000017	0.282979	7.4	10.4	0.6130	391	526	−0.94
JCH7-01	0.094189	0.003074	0.282460	0.000009	0.282433	−11.2	−1.7	0.3222	1185	1547	−0.91
JCH7-02	0.051648	0.001681	0.282379	0.000009	0.282364	−14.0	−4.2	0.3072	1256	1701	−0.95
JCH7-03	0.068687	0.002260	0.282392	0.000009	0.282372	−13.6	−3.9	0.3333	1257	1682	−0.93
JCH7-04	0.062284	0.002013	0.282408	0.000010	0.282390	−13.0	−3.2	0.3404	1225	1642	−0.94
JCH7-05	0.076636	0.002472	0.282392	0.000009	0.282370	−13.5	−4.0	0.3094	1264	1687	−0.93

Notes:ε_Hf(t) = 10⁴ × {[(¹⁷⁶Hf/¹⁷⁷Hf)_S − (¹⁷⁶Lu/¹⁷⁷Hf)_S × (e^λt − 1)]/[(¹⁷⁶Hf/¹⁷⁷Hf)_CHUR − (¹⁷⁶Lu/¹⁷⁷Hf)_CHUR × (e^λt − 1)] − 1}, t_DM = 1/λ × ln{1 + [(¹⁷⁶Hf/¹⁷⁷Hf)_S − (¹⁷⁶Hf/¹⁷⁷Hf)_DM]/[(¹⁷⁶Lu/¹⁷⁷Hf)_S − (¹⁷⁶Hf/¹⁷⁷Hf)_DM]}. t_CD^M = t_DM − (t_DM-t) × [(f_cc − f_s)/(f_cc − f_DM)]. f_Lu/Hf = (¹⁷⁶Lu/¹⁷⁷Hf)_S/(¹⁷⁶Lu/¹⁷⁷Hf) _CHUR-1. Among them: λ = 1.876 × 10⁻¹¹a⁻¹; (¹⁷⁶Lu/¹⁷⁷Hf)_Sand(¹⁷⁶Lu/¹⁷⁷Hf)_S are sample measurements; (¹⁷⁶Lu/¹⁷⁷Hf) _CHUR = 0.332, (¹⁷⁶Hf/¹⁷⁷Hf) _CHUR = 0.282772([25]); (¹⁷⁶Hf/¹⁷⁷Hf)_DM = 0.0384, (¹⁷⁶Hf/¹⁷⁷Hf)_DM = 0.28325; (¹⁷⁶Hf/¹⁷⁷Hf) _{average crustal thickness} = 0.015([26]); f_cc = [(¹⁷⁶Lu/¹⁷⁷Hf)_{average crustal thickness}/(¹⁷⁶Lu/¹⁷⁷Hf) _CHUR]-1; f_s = f_Lu/Hf; f_DM = [(¹⁷⁶Lu/¹⁷⁷Hf) _DM /(¹⁷⁶Lu/¹⁷⁷Hf) _CHUR] − 1; t refers to the crystallization age of zircon.

. Zircon Lu-Hf isotope analysis data show that the early Paleozoic zircon ¹⁷⁶Yb/¹⁷⁷Hf ratio was between 0.051648 and 0.094189, the average was 0.073504, the ¹⁷⁶Lu/¹⁷⁷Hf ratio was between 0.001681 and 0.003074, and the average was 0.002402; the late Triassic zircon ¹⁷⁶Yb/¹⁷⁷Hf ratio was between 0.034114 and 0.069213, the average was 0.052969, the ratio of ¹⁷⁶Lu/¹⁷⁷Hf was between 0.001293 and 0.002607, and the average was 0.002018; the ratio of Early Cretaceous zircon ¹⁷⁶Yb/¹⁷⁷Hf was between 0.024444 and 0.060041, the average was 0.042568, the ratio of ¹⁷⁶Lu/¹⁷⁷Hf was between 0.000857 and 0.002276, and the average was 0.001608. The ratio of ¹⁷⁶Lu/¹⁷⁷Hf of all zircon analysis points was less than 0.004, indicating that after the formation of zircon, there was only a small amount of radioactive Hf accumulation. Therefore, the initial ¹⁷⁶Hf/¹⁷⁷Hf ratio obtained by analysis and testing can be used to represent the Hf isotope composition of the system when zircon was formed.

The Hf isotope calculation was based on the age of a single zircon. As shown in the frequency distribution histogram of zircon εHf(t) values (Figure 10a), the range of zircon εHf(t) value changes of three different ages were compared. The zircon εHf(t) values of the Early Paleozoic age were between −4.69 and −1.71, the average was −3.49, and they were mainly distributed between −3 and −5; the zircon εHf(t) values of the Late Triassic age were between 2.4 and −13.0, the range of variation was large, and the average was 8.8; the zircon εHf(t) values of the Early Cretaceous age were between 1.4 and 10.4, and the average was 5.5. In the characteristic map of zircon Hf isotopic composition (Figure 10b), the casting points of zircons of the Late Triassic and Early Cretaceous ages were found to fall between the chondrite evolution line and the depleted mantle evolution line. The single-stage Hf isotope model age TDM was found to range between 350 and 781 Ma, with averages of 523 Ma and 391 to 750 Ma obtained. The two-stage Hf isotope model ages of TCDM were found to range between 428 and 1093 Ma, with averages of 694 Ma and 526 to 1104 Ma obtained.

6. Discussion

6.1. Time Limits of Diagenesis

The diabase in the study area is an intrusive rock mass closely symbiotic with the ore body. However, estimates of its precise isotopic age limits are limited [1]. Previous stratigraphic studies have indicated the diabase to be a Hercynian intrusive rock mass. In this study, the U-Pb ages of zircons obtained by LA-ICP-MS were determined to be 216.9 ± 2.7 Ma and 213.9 ± 2.9 Ma, thus indicating that emplacement crystallization of the Jinchanghe diabase occurred in the Late Triassic. This result is consistent with the time limits of the closing of the ancient Tethys Ocean [27]. The extension or extensional structure of the Baoshan block could be attributed to collisional orogeny between the Baoshan and Simao blocks. These structures caused an upwelling of the basic mantle source magma to form the diabase intrusion during this time limitation.

In this study, the U-Pb age of the hydrothermal zircon was determined to be 130.5 ± 8.8 Ma, thus indicating the occurrence of strong hydrothermal activity or mineralization during this time zone. The results also suggest that the metallogenic time limit of the Jinchanghe Fe-Cu-Pb-Zn polymetallic deposit is Early Cretaceous. This age is consistent with the Rb-Sr isochron line age of sphalerite (117–120 Ma) [5], thus providing further evidence for the metallogenic time limits of the Jinchanghe Fe-Cu-Pb-Zn polymetallic deposit. Previous research in the study region has indicated the Rb-Sr isochronic ore-forming ages of the Hetaoping and Luziyuan Pb-Zn deposits to be 116.1 ± 3.9 Ma [11] and 141.9 ± 2.6 Ma [28], respectively. These results are consistent with the hydrothermal zircon age (136.3 ± 9.4 Ma) obtained in this study and suggest that the typical representative Pb-Zn polymetallic deposits in the region are products of geological events in the same period.

6.2. Tectonic Environment

The basic rock wall resulted from the rapid emplacement of magma from a deep source to the shallow part of the crust due to tectonic continental crust extension [29]. Therefore, the study of the geochemical characteristics and chronology of the basic rock can elucidate its geotectonic background and formation time limits.

In this study, basalt-type geotectonic environments were classified as oceanic and continental and were found to be characterized by a Th/Ta ratio of 1.6 for the original mantle. Basalt in the continental plate is divided across the continental rift and the internal thermal column. The Th/Ta ratio of the Jinchanghe diabase was found to range from 1.12 to 4.38, with an average of 1.96 obtained, indicating a wide range of variation. The Ta/Hf ratio of the diabase was found to range between 0.44 and 2.02, with an average of 0.79 obtained, which indicated that the Jinchanghe diabase presented characteristics of continental rift basalt. Furthermore, the trace element tectonic environment discrimination diagram (Figure 11) indicated that all sample points for the Jinchanghe diabase were plotted on the within-plate basalt area, thus suggesting that the rocks indicated characteristics of within-plate basalt. In addition, the Jinchanghe diabase lacked HFSEs, which is consistent with the characteristics of continental rift basalt [30]. Therefore, considering the diabase distribution near the transtensional fault, these results suggest that the Jinchanghe diabase was formed in an extensional tectonic setting.

6.3. Magma Sources

The geochemical properties of basalts are predominantly affected by the composition of the mantle region from which they are derived. Additionally, their composition varies with the tectonic setting [31]. The ratio of highly incompatible elements is generally stable during the process of magma separation and partial melting. Therefore, end-member types of ocean island basalts (OIB) are often distinguished by ratios of highly incompatible elements such as Th, Ta, Nb, Ba, Rb, and La. According to the Hofmann mantle model, the OIBs can be divided into three different end members: HIMU OIB, EMI OIB, and EMII OIB [32]. Weaver concluded that the HIUM OIB was derived from the subduction of the ancient oceanic shell to the lower mantle, while the EMI OIB and EMII OIB originated from the subduction and dehydration of the ancient oceanic crust, respectively. Moreover, EMI OIB is characterized by the presence of deep-sea sediments, while EMII OIB is characterized by the occurrence of terrigenous clastics [33].

All points in the Ta/Yb-Th/Yb diagram (Figure 12) were plotted on the enriched mantle source area, thus indicating that the Jinchanghe diabase was formed by the partial melting of the enriched mantle. A comparison of ratios between them and OIB terminal elements and the major incompatible elements (

Table 5. The ratios of incompatible elements of diabase and mantle endmember and main chemical reservoirs in the Jinchanghe Fe-Cu-Pb-Zn deposit.

	Zr/Nb	La/Nb	Ba/Nb	Ba/Th	Th/Nb	Th/La	Ba/La	Data Source
Primitive mantle	14.8	0.94	8	77	0.12	0.13	9.6	Weaver, B.L. 1991 [33]
Depleted mantle	30	1.07	4.3	60	0.07	0.07	4
Continental crust	16.2	2.2	54	124	4.7	0.2	25
HIMU OIB	3.2~5	0.66~0.77	4.9~6.5	49~77	0.35~0.38	0.107~0.133	6.8~8.7	Plank, T., C. H. and Langmuir, C.H. 1998 [34]
EMI OIB	5~13.1	0.78~1.32	9.1~23.4	80~204	0.69~1.41	0.089~0.147	11.2~19.1
EMII OIB	4.4~7.8	0.79~1.01	6.4~11.3	57~105	0.58~0.87	0.108~0.183	7.3~13.5
Diabase of Jinchanghe	1.73~14.69	0.63~1.29	1.04~44.74	8.31~169.42	0.08~0.28	0.12~0.22	1.49~35.98	This paper
Average	5.73	0.81	9.01	67.54	0.13	0.15	10.35

) suggests that the Jinchanghe diabase belongs to the enriched HIMU mantle.

The Mg^# values of the Jinchanghe diabase ranged between 48.22 and 71.21, with an average of 56.42 obtained. Additionally, the Mg^# standard values of between 68 and 75 were lower than those of the original magma and indicated an association with moderately evolved magma [35]. The Th/Ta ratio of the Jinchanghe diabase ranged between 1.12 and 4.38, with an average of 1.96 obtained, while the Th/Ta ratios of the original mantle and continental crust are known to be 2.3 and 10 [24], respectively, thus suggesting that the Jinchanghe diabase was less likely to be contaminated by the Earth’s crust. Additionally, the Zr/Hf ratio of the Jinchanghe diabase ranged between 15.81 and 36.84, with an average of 31.78 obtained, which are higher values than those obtained for the crust (11) and close to those obtained for the original mantle (36.73) [33]. Therefore, it is less likely that the Jinchanghe diabase was contaminated by crustal materials.

Previous studies have shown that the Lu-Hf isotope group in zircon can better indicate the source of magma and its mixing process. The analysis results of the Hf isotopic composition of the Jinchanghe diabase zircon show that the εHf(t) values of the magmatic zircon and the hydrothermal zircon ranged, respectively, between 2.4 and 13.0 and 1.4 and 8.1, both of which are positive. The age of TCDM (428–1093Ma, 526–1104 Ma) was found to be greater than the crystallization age (182–233 Ma, 124–144 Ma). In the zircon t-εHf(t) diagram, all sample casting points fall below the depleted mantle evolution line. The above characteristics indicate that the magma source area of the Jinchanghe diabase either was contaminated by ancient crustal materials or originated from the enriched mantle. There are obvious inheritance or capture zircons on the zircon CL. The crystallization age of the inherited or captured zircon was determined to be between 497 ± 11 and 448 ± 6 Ma, which is the same as the crystallization age of the granite body in the Baoshan block (447–486 Ma) [36]. Further, its εHf(t) values ranged between −5.5 and −1.3. On the zircon t-εHf(t) diagram, all points are placed under the chondrite evolution line, indicating that the parent magma that inherits or captures zircon originated from the partial melting of ancient crustal material. Based on the above characteristics, it is believed that the Jinchanghe diabase originated from an enriched mantle source area and may have been contaminated by crustal materials during the ascent of magma.

Finally, the cathodoluminescence map of zircon indicated that the internal structure of magmatic zircon in the Jinchanghe diabase was uniform, and no early formation of zircon tuberculosis was observed. These results also indicate that it is less likely that the Jinchanghe diabase was contaminated by the Earth’s crust [37]. This could be attributed to the faster emplacement of magma in the upward direction, which could have resulted in a lower degree of contamination by the Earth’s crust. In summary, the Jinchanghe diabase magma originated from the enriched mantle, which was less likely to be contaminated by crustal materials during magma evolution and predominantly reflected characteristics of the source zone.

6.4. Regional Tectonic-Magma Evolution and Mineralization

Previous studies have indicated that the Baoshan block experienced the geological tectonic evolution of the ancient Tethys, the central Tethys, and the new Tethys [38]. The structure in the area is relatively developed, and magmatism is frequent.

The Paleo-Tethys oceanic plate subduction and orogenic formation in the Early Paleozoic (502–448 Ma) formed the Pinghe adamellite [14,15,16,17]. The Baoshan block experienced a quiet period of magmatism from 440 to 270 Ma. Notably, the Gengma monzonitic granite rock mass developed on the southeastern margin of the Baoshan block; its U-Pb age has been determined to be between 232 and 230 Ma, and its genesis was related to the closure of the Paleo-Tethys Ocean [39]. The Paleo-Tethys Ocean closed in the Late Triassic and the oceanic crust subducted beneath the Qiangtang-Baoshan block. Additionally, the oceanic crust partially melted to generate the basic magma. Subsequently, magma rising and emplacement along the weak tectonic fault zone formed the diabase. Combined with zircon U-Pb dating data of this study, it shows that Jinchanghe diabase is the product of Late Triassic magmatic activity. The magmatic activity and mineralization in the Early Cretaceous were relatively developed. The closure of the Middle Tethys Ocean affected the thickening of the crust on the western side of the Baoshan block, which led to the re-melting of the crust and consequent initiation of magmatism, mixed lithification, and mineralization. The magmatic event during this period was mainly represented by the development and formation of the Zhibenshan biotite granite and the Kejie biotite granite in the northwest Baoshan block. The zircon U-Pb age of the Zhibenshan granite has been determined to be 126.7 ± 1.6 Ma, while that of the Kejie biotite granite, which formed in the shear extension structure of the Middle Tethys Ocean, has been determined to be 93 ± 13 Ma. This has further been related to the deep melting of the crustal material caused by the thickening of the Earth’s crust [40]. In this study, the hydrothermal zircon U-Pb age of the Jinchanghe diabase was determined to be 130.5 ± 8.8 Ma, which indicates that the mining area experienced a strong hydrothermal event in the Early Cretaceous. Considering the regional tectonic evolution, the Bangonghu-Nujiang Ocean of the Middle Tethys closed in the Early Cretaceous, and the collision between the Tengchong and Baoshan blocks formed the Gaoligong collisional tectonic belt [41,42]. Additionally, the collision resulted in internal crustal thickening and periodic shearing in the interior of the Baoshan block [43]. Therefore, it is speculated that the formation of the Jinchanghe Fe-Cu-Pb-Zn polymetallic deposit was related to tectonic-magmatic events caused by the shortening and thickening of the inner crust of the Baoshan block in the Early Cretaceous.

7. Conclusions

(1)

The zircon U-Pb ages of the Jinchanghe diabase were found to be 216.9 ± 2.7 Ma, 213.9 ± 2.9 Ma, and 130.5 ± 8.8 Ma, thus indicating that the region experienced two-stage tectonic-magmatic events in the Late Triassic and Early Cretaceous. The Late Triassic represented the crystallization and emplacement stages of the diabase, while the Early Cretaceous represented the hydrothermal zircon formation period after the hydrothermal superposition reformation.

(2)

The tectonic environment discrimination diagram of strongly incompatible elements suggested that the Jinchanghe diabase was characterized by a series of calc-alkaline basalts from the continental plate and was formed during the upwelling of mantle materials under extensional tectonic settings. Moreover, the magma indicated fast upward emplacement. Thus, it was less likely to be contaminated by the crust and predominantly reflected characteristics of the source region.

(3)

The Paleo-Tethys Ocean closed in the Late Permian-Late Triassic, and the Burmese-Thaima micro-continent (the Baoshan block) collided with the main body of the Simao block. The collisional orogenic effects resulted in stretching inside the Baoshan block, and the Jinchanghe basic primitive magma was raised along the weak tectonic fault zone to form the diabase during this period.

(4)

The closure of the Middle Tethys Ocean in the Early Cretaceous resulted in a collision between the Baoshan and Tengchong blocks. Consequently, crustal thickening and shearing extension occurred inside the Baoshan block, which experienced a strong hydrothermal event. This enabled the formation of the Jinchanghe Fe-Cu-Pb-Zn polymetallic deposit.