Genesis of Gypsum/Anhydrite in the World-Class Jinding Zn-Pb Deposit, SW China: Constraints from Field Mapping, Petrography, and S-O-Sr Isotope Geochemistry

Abstract

The world-class Jinding deposit in SW China has ~15 Mt of Zn and Pb metals combined, in an evaporite dome containing amounts of gypsum/anhydrite. These gypsum and anhydrite are mainly located in limestone breccias (Member I), gypsum-bearing complexes (Member III), and red mélange, with some occurring as veins in clast-free sandstone (Member IV) and as fractures/vugs of host rock. The gypsum/anhydrite and dome genesis remain equivocal. The gypsum in limestone breccias and in red mélange with flow texture contains numerous Late Triassic Sanhedong limestone fragments. The δ³⁴S (14.1%–17%), δ¹⁸O (9.7%–14.6%), and ⁸⁷Sr/⁸⁶Sr ratios (0.706913–0.708711) of these gypsum are close to the S-O-Sr isotopes of the Upper Triassic Sanhedong Formation anhydrite in the Lanping Basin (δ³⁴S = 15.2%–15.9%, δ¹⁸O = 10.9%–13.1%, ⁸⁷Sr/⁸⁶Sr = 0.707541–0.707967), and are inconsistent with the Paleocene Yunlong Formation gypsum in the Lanping Basin (⁸⁷Sr/⁸⁶Sr = 0.709406–0.709845), indicating that these gypsum were derived from the Upper Triassic Sanhedong Formation evaporite but not from the Paleocene Yunlong Formation, and formed as a result of evaporite diapirism. The δ³⁴S (14.3%–14.5%), δ¹⁸O (10.1%–10.3%), and ⁸⁷Sr/⁸⁶Sr ratios (0.709503–0.709725) of gypsum as gypsum–sand mixtures in gypsum-bearing complexes are similar to the ⁸⁷Sr/⁸⁶Sr ratios of gypsum in the Yunlong Formation of the Lanping Basin and Cenozoic basins in the northern part of the Himalayan–Tibetan orogen, suggesting that the material source of this gypsum was derived from the Yunlong Formation, and formed as a result of gypsum–sand diapirism. The gypsum veins in clast-free pillow-shaped mineralized sandstone and the gypsum in host rock fractures and vugs formed after the supergene minerals such as smithsonite. The δ³⁴S (−16.3%~−12.7%) and δ¹⁸O (−9.8%~−4.7%) of this gypsum indicate that the gypsum is of supergene origin with sulfate derived from the reoxidation of reduced sulfur. We confirmed that the Jinding dome is genetically related to diapir of the Late-Triassic Sanhedong Formation evaporite. Clast-free sandstone and gypsum-bearing complexes in the dome were produced by diapir of the Paleocene Yunlong Formation unconsolidated gypsum–sand mixtures.

1. Introduction

Mississippi Valley-type (MVT) Pb–Zn deposits are mainly hosted in carbonate rocks and typically have no obvious genetic association with igneous activity. The most important ore controlling factors are a carbonate/evaporite dissolution–collapse structure, pre-existing barite, porous dolostone and an evaporite diapiric structure [1,2]. However, due to the solubility of evaporite or it being replaced by calcite, silica, and barite, the evaporite diapiric structure does not receive enough attention.

The world-class Jinding Zn–Pb deposit contains ~200 Mt ore, at 6.1% Zn and 1.3% Pb, and is the world’s third-largest MVT Zn–Pb deposit [3]. The orebodies of the Jinding deposit are hosted within a dome consisting of a series of complex rocks, including clast-free and limestone clast-bearing sandstones, gypsum-bearing complexes, and limestone breccias containing amounts of gypsum and anhydrite. Nevertheless, the genesis of Jinding dome remains controversial [4,5,6,7,8,9]. Early studies considered that the Jinding dome was related to thrust nappe structure, which formed sliding–collapse breccia and coarse clastic rocks of alluvial facies as the ore-hosting rock [4,5]. The limestone clast-bearing sandstones and limestone breccias were treated as a part of the Paleocene Yunlong Formation, whereas clast-free sandstones were assigned to the Early Cretaceous Jingxing Formation, which formed in an alluvial fan environment [4,5,6,7], maintaining that the gypsum and anhydrite in Jinding deposit were formed in sedimentary environment. Recent field observation and mineralogical mapping suggested that the Jinding dome was created by a diapiric migration of Lower Triassic evaporite during Paleocene thrust loading [8,9], and maintain that evaporite diapir structures are common and important for the Zn–Pb mineralization. The gypsum and anhydrite in the Jinding deposit were formed in a diapiric environment. Consequently, the genesis of gypsum/anhydrite in the Jinding dome is important to understand the formation mechanism of the Jinding dome and ore host rocks. Unfortunately, there are no detailed studies available on the genesis of gypsum/anhydrite in deposit.

In this contribution, a detailed investigation of the gypsum/anhydrite has been carried out on the Jinding deposit based on field mapping, drill core assay and petrological observation. We further used LA–ICP–MS in situ Sr isotope and whole-rock S-O isotope analysis to constrain the genesis of gypsum/anhydrite. In addition, we discussed the evolution of Jinding dome and evaporite diapirs, which are significant to understanding the geological background of Jinding deposit.

2. Regional Geology

The Jinding Zn–Pb deposit is located in the Lanping Basin of the northern Lanping–Simao block in the eastern Himalayan–Tibetan orogen, SW China (Figure 1). The Lanping Basin is structurally bounded by the Cenozoic Diancangshan–Ailaoshan shear zone and the Cenozoic Chongshan shear zone (Figure 2), and contains a thick section of Permian–Neogene sedimentary rocks with some igneous rocks. Lower Permian to Middle Triassic volcanic rocks and siliciclastic rocks with a minor amount of carbonates, thought to have formed as a result of the eastwards subduction of the Paleo-Tethys Ocean beneath the Lanping–Simao block, are exposed along the basinal margins [10,11,12]. With the Paleo-Tethys Ocean closure and the subsequent terrane collision, Late Triassic pelagic fine-grained siliciclastic and marine carbonate rocks were deposited with a density of over 1600 m in a foreland basin [13]. During the Jurassic to Cretaceous, terrestrial red clastic rocks were deposited with a density of over 2000 m in a depression basin under a regional compression environment [14,15,16]. During the Cenozoic, the India–Asia continental collision led to folding, thrusting, and subsequent strike-slipping in the Lanping–Simao block. Red terrestrial siliciclastic rocks, including siltstone, mudstone, sandstone, and conglomerate, were deposited in the Basin [14].

Evaporites, mainly gypsum, anhydrite and minor halite, commonly occur within the Late Triassic limestone sequence and the Paleocene red siliciclastic rocks. This indicates a long-term arid environment in the Lanping Basin, especially in early Paleogene when a thickness of evaporate-bearing sequences was formed [17]. The locally irregular gypsum/anhydrite bodies with flow and diapir structures and aligned T₃s limestone clasts occur in the basin, indicating that the gypsum may have been generated by the diapirism of the Late Triassic evaporite sequence [8].

The world-class Jinding Zn–Pb–Sr deposit and over 100 Pb–Zn–Ag–Cu deposits are located in the Lanping Basin. The latter includes carbonate–Pb–Zn sulfide veins in Jurassic to Cretaceous clastic rocks in the northern segment of the Lanping Basin, MVT Zn–Pb deposits in carbonate [18,19], and vein-type Cu sulfide mainly along the western basinal margin [20,21] (Figure 2).

Figure 1. (A) Generalized structural system of the eastern Himalayan–Tibetan orogen. (B) Simplified geologic map showing the distribution of the Zn–Pb deposit and Mesozoic–Cenozoic basins in the Himalayan–Tibetan orogen (modified from [9,22]).

Figure 1. (A) Generalized structural system of the eastern Himalayan–Tibetan orogen. (B) Simplified geologic map showing the distribution of the Zn–Pb deposit and Mesozoic–Cenozoic basins in the Himalayan–Tibetan orogen (modified from [9,22]).

Figure 2. Simplified geological map showing the distribution of Jinding Zn–Pb–Sr deposit and Cu-Zn–Pb–Sr deposits in Lanping Basin (modified after [16,21]).

Figure 2. Simplified geological map showing the distribution of Jinding Zn–Pb–Sr deposit and Cu-Zn–Pb–Sr deposits in Lanping Basin (modified after [16,21]).

3. Geology of Jinding Deposit

The Jinding Zn–Pb deposit is hosted within a tectonic dome consisting of Paomaping, Beichang, Jiayashan, Fengzishan, Xipo, Nanchang, and Baicaoping ore blocks (Figure 3A). Open pit comprises Beichang and Jiayashan and covers >90% of the Zn and Pb reserves in the deposit. A new geological mapping of the open pit divided the Jinding dome rocks into three main structural units: Lower, Middle, and Upper units, respectively [9] (Figure 4).

The Upper Unit is an allochthonous thrust slice and comprises the inverted sequence of Middle Jurassic and Upper Triassic sedimentary rocks. In detail, Middle Jurassic rocks are the Huakaizuo Formation red mudstone and siltstone (J₂h), and the Late Jurassic rocks are the Bazhulu Formation mudstone and siltstone (J₃b). The Upper Triassic strata include the Waigucun Formation (T₃w?) muddy siltstone, the Sanhedong Formation limestone (T₃s), and the Maichuqing Formation mudstone and siltstone (T₃m; Figure 4).

The Middle Unit comprises mainly brecciated limestone, limestone clast-bearing and un-brecciated sandstones, separated from the Upper Unit by thrust faults. The brecciated limestone consists of angular T₃s limestone clasts in a matrix that contain fine-grained limestone fragments and calcite. This member contains irregularly shaped gypsum, anhydrite, and sandstone bodies, which display diapir and injection features and contain aligned limestone fragments. Gypsum bodies formed on the surfaces of some of the rocks, whereas anhydrite units are well preserved underground and can reach >100 m thick in places. These limestone breccias transition to sandstones in the lower part towards the west of the Beichang block; upwards, the sandstones outnumber the breccias in the Baicaoping block. The limestone clast-bearing sandstones contain well-orientated clasts of the T₃s limestone, generally smaller than 5 cm in diameter and containing sedimentary structures such as bedding, mud cracks, and wave ripples. The limestone breccias and the limestone clast-bearing sandstones are overlain by a gypsum-bearing complex that comprise a matrix of lenticular gypsum, detrital sand grains with limestone clasts. Locally, there are gypsum bodies containing detrital quartz grains and limestone clasts. Above this complex is clast-free sandstone, the most important ore host in Jinding (Figure 4). This member consists of a clast-free sandstone and locally contain pillow-shaped quartz grain-bearing gypsum bodies which form thinly laminated layers and crosscut quartz grains without any sedimentary textures. Sand veins connected with the sandstone have penetrated the overlying J₂h mudstone and siltstone in places.

The Lower Unit consists of the Late Cretaceous Hutoushi Formation sandstone (K₂h) and overlying sandstones that have sedimentary bedding and contain variable amounts of small T₃s limestone have brecciated (generally <1 cm in diameter).

A gypsum-bearing mélange is exposed in the east of Jinding open pit in addition to these rocks, and is assigned to the Paleocene Yunlong Formation (E₁y). Above this mélange is the Eocene Guolang Formation sandstone and siltstone (E₁g).

The vast majority of the Zn–Pb sulfides are hosted in the Middle Unit with a concentration mostly of bleached sandstone (Figure 4). Of the overall Zn and Pb reserves of the deposit, ~56% is hosted by bleached sandstones, and ~44% is hosted by brecciated limestone, with ~90% of which occurring in the form of near-surface supergene Zn and Pb non-sulfides. The zinc and lead mineralization is continuous and contains disseminated sphalerite and galena that have replaced the pre-ore calcite matrix in the bleached sandstones. In the gypsum-bearing complex and the limestone breccias, Zn–Pb sulfide mineralization is characterized by replacement and open spaces-filling styles in the form of textured colloform [9]. Huang et al. (2022) suggested a pyrite Re–Os isochron age of 25.6 ± 3.6 Ma for the Jinding Zn–Pb mineralization, which is broadly coeval with the paleomagnetic age (23 ± 3 Ma) and apatite fission-track age (28–25 Ma) [24,25].

It is summarized that gypsum and anhydrite in the Jinding deposit is confined to the limestone breccias, clast-free sandstone, gypsum-bearing complex, and red mélange within the Middle Unit. The limestone breccias-hosted gypsum and anhydrite generate 2.12 Mt ore at a grade of 76.63% (in terms of CaSO₄). In addition, trace amounts of transparent gypsum fill vugs in limestone breccias and smithsonite in a colloform. The characteristics and genesis of different types of gypsum/anhydrite are variational.

4. Sampling and Methods

4.1. Mapping, Drill Core Assay and Samples

This study mapped the gypsum/anhydrite distribution zone in the Jinding open pit. When a rock containing >~50% vol. gypsum/anhydrite has the volume of >1 m³, the coordination of this site was recorded using a Magellan eXplorist 610 GPS unit (precision better than 5 m). Drill cores were investigated to determine the distribution of gypsum/anhydrite in the Baicaoping block.

Different types of gypsum/anhydrites (including supergene gypsum, to be described later) were sampled from the Jinding open pit, along with drill cores in the Baicaoping block for petrography observation, in situ Sr isotope and whole-rock S-O isotope analyses. Sample locations are shown in Figure 3B,C and Figure 4.

4.2. Petrography

Polished 30 μm-thick and 100 μm-thick thin sections were used for petrographic observations with optical and backscattered electron (BSE) microscopy for in situ Sr isotope analyses. BSE images were taken using an FEI Nova Nanosem-450 microscope (Thermo Fisher Scientific, Waltham, MA, USA) equipped with an energy-dispersive spectrometer (EDS), at the Institute of Geology, Chinese Academy of Geological Sciences (CAGS), Beijing, China.

4.3. In Situ Sr Isotope Analysis

In situ Sr isotope analysis for gypsum and anhydrite on polished 100 μm-thick thin sections were conducted using a Resolution laser ablation (LA) system coupled to a Nu Plasma II multi-collector (MC) ICP–MS at the State Key Laboratory of Geological Processes and Mineral Resource (GPMR), China University of Geosciences (Wuhan, China). The analyses used 130 μm spot size, 12 Hz repetition rate, and 4.5 J/cm² energy density. An in-lab coral was used as an external standard. The average 87Sr/86Sr value for coral standard is 0.70922 ± 0.00005, which is consistent with the recommended value (0.70923 ± 0.00002) determined by ID–TIMS at the MDR [26].

4.4. Sulfur and Oxygen Isotope Analyses

Whole-rock S-O isotope analyses of gypsum and anhydrite were determined at the Center of Analysis, Beijing Research Institute of Uranium Geology, Beijing, China. After acid pickling to remove sulfide and carbonate, sulfate samples were dissolved and reacted with BaCl₂, and then converted to purity BaSO₄. For sulfur isotope analysis, 2 mg of solid barite were weighed into a silver capsule and converted to SO₂ using V₂O₅ and SiO₂ as reactants at 980 °C. For the oxygen isotope analysis, 100 mg of solid barite were weighed, and samples were introduced into a graphite furnace at 1000 °C to produce CO [27]. The SO₂ and CO were then transferred into a Delta Plus mass spectrometer, respectively, for S–O isotope analyses. The international standards NBS-127 (+9.37%, VSMOW) for oxygen isotope and NBS-127 (+20.42%, VCDT), IAEA-SO-5 (+0.30%, VCDT), and IAEA-SO-6 (−34.01%, VCDT) for sulfur isotope were used to monitor the accuracy of the results. Repeated measurements of these international standard materials yielded analytical accuracy of 0.1% for both the oxygen and sulfur isotope measurements.

5. Results

5.1. Distribution of Gypsum and Anhydrite and Their Petrography

Member I in Middle Unit, brecciated limestones: this member contains ubiquitous irregularly shaped gypsum/anhydrite bodies. There is gypsum in the Beichang–Jiayashan open pit, but it is poorly preserved. In contrast, there are large amounts of anhydrite in the Paomaping and Baicaoping undergrounds, which are the main source of CaSO₄ in the Jinding deposit. Anhydrite is present as the breccia matrix with flow texture (Figure 5A,B) and displays typical evaporite diapirism [8]. One anhydrite-rich body can be >100 m thick and several hundred meters long.

Red mélange: gypsum in this member is present as irregular shaped bodies with T3s limestone fragments in muddy and silty matrix (Figure 5C,D).

Member III, gypsum-bearing complex: the gypsum in this area occurs in mixtures with sand (Figure 6A,B).

Member IV, clast-free sandstone: the gypsum in this member present as thinly laminated layers within pillow-shaped bodies where gypsum veins crosscut quartz grain (Figure 6C,D).

Vugs and fractures: this transparent gypsum mainly fills in vugs in limestone breccia and smithsonite, representing supergene origin (Figure 6E,F).

It is worth noting that celestine is common in gypsum and anhydrite samples (Figure 7), which can significantly affect the analytical results of the whole-rock Sr isotope. In situ analyses can allow gypsum and anhydrite to avoid contamination from celestine mineralization [28].

5.2. Strontium Isotopes

In situ ⁸⁷Sr/⁸⁶Sr compositions for gypsum/anhydrite and collected whole-rock Sr isotopes for gypsum in the Paleocene Yunlong Formation of the Lanping Basin and Cenozoic basins of the northern part of the Himalayan–Tibetan orogen are presented in Figure 8 and Supplementary Table S1. The Upper Triassic Sanhedong Formation anhydrite displays homogeneous ⁸⁷Sr/⁸⁶Sr values, with a relatively narrow range from 0.707541 to 0.707967, which is similar to Triassic seawater [29,30].

The Sr isotope compositions for gypsum/anhydrite in limestone breccias and red mélange show slightly variable ⁸⁷Sr/⁸⁶Sr values that range from 0.706913 to 0.708711, which are close to Sr isotope of the Upper Triassic Sanhedong Formation anhydrite in the Lanping Basin and significantly lower than the Sr isotope of gypsum in the Paleocene Yunlong Formation of the Lanping Basin. The gypsum in the gypsum-bearing complex and clast-free sandstone displays homogeneous ⁸⁷Sr/⁸⁶Sr values range from 0.709503 to 0.709725 and 0.710497 to 0.710568, respectively. This limited variation is consistent with the reported whole rock Sr isotope ratios (0.709406–0.710049, and 0.708114–0.710071, respectively) for gypsum in the Paleocene Yunlong Formation of the Lanping Basin and Cenozoic basins of northern part of the Himalayan–Tibetan orogen [23,31,32].

The ⁸⁷Sr/⁸⁶Sr ratios of celestine in gypsum samples are 0.710126 to 0.710198, more radiogenic than that of the limestone breccias-hosted gypsum/anhydrite.

5.3. Sulfur and Oxygen Isotopes

Whole rock S and O isotope compositions for gypsum/anhydrite in the Jinding deposit and collected whole-rock S–O isotopes for gypsum in the Paleocene Yunlong Formation of the Lanping Basin are presented in Figure 9 and Supplementary Table S2. The δ³⁴S and δ¹⁸O values of gypsum in limestone breccias are of 15.1 to 17% and 9.7 to 14.6%, in good agreement with the Upper Triassic Sanhedong Formation anhydrite (δ³⁴S = 15.2 to 15.9% and δ¹⁸O = 10.9 to 13.1%). Gypsum in red mélange has δ³⁴S = 14.3 to 14.6% and δ¹⁸O = 9.1 to 9.3%, slightly lower than those of the Sanhedong Formation anhydrite. The δ³⁴S and δ¹⁸O values of gypsum in gypsum-bearing complexes are of 14.1 to 14.5% and 10.1 to 10.3%, which is similar to the reported S and O isotopes of the Paleocene Yunlong Formation (δ³⁴S = 13.4 to 15.2% and δ¹⁸O = 6.6 to 16.8%, mainly vary from 8 to 13%) and the Upper Triassic Sanhedong Formation. Gypsum in clast-free sandstone and fracture/void has δ³⁴S = −16.3% to −12.7% and δ¹⁸O = −9.8% to −4.7%, apparently lower than those of the other types of gypsum and anhydrite in the Jinding deposit.

6. Discussion

6.1. The Genesis of Different Type Gypsum/Anhydrite

Different types of gypsum and anhydrite in the Jinding deposit have various formation mechanisms. The δ³⁴S, δ¹⁸O and in situ ⁸⁷Sr/⁸⁶Sr ratios of gypsum/anhydrite in limestone breccias and red mélange are close to S–O–Sr isotopes of the Upper Triassic Sanhedong Formation anhydrite from the Lanping Basin, and are inconsistent with Paleocene Yunlong Formation gypsum in Lanping Basin. Combined with the characteristics of the gypsum/anhydrite present as the breccia matrix with flow textures and injection features, we maintain that this gypsum/anhydrite derived from the Upper Triassic Sanhedong Formation evaporite but not from the Paleocene Yunlong Formation. Our new data are consistent with Song et al. (2020)’s interpretation based on geological mapping, that the gypsum/anhydrite formed as a result of the diapirism of the Upper Triassic evaporites under the regional compression environment [9].

The δ³⁴S, δ¹⁸O and ⁸⁷Sr/⁸⁶Sr ratios of gypsum in gypsum-bearing complexes are similar to the S–O–Sr isotopes of gypsum in the Paleocene Yunlong Formation of the Lanping Basin and Cenozoic basins of northern part of the Himalayan–Tibetan orogen. Geological mapping in Jinding suggests that this member was produced by evaporite and gypsum-sandstone diapirism [9]. Our new geochemical data are consistent with this interpretation and further suggest that this gypsum was derived from the Yunlong Formation, and formed as a result of unconsolidated gypsum–sandstone diapirism during thrust loading and the Yunlong Formation sedimentation.

The vein gypsum in clast-free pillow-shaped mineralized sandstone and the gypsum in vugs display depleted the sulfur and oxygen isotope compositions and formed after supergene minerals such as smithsonite. In Jinding, the interaction between organic fluids and evaporites occurred and formed H₂S by the bacterial reduction of sulfate (BSR) [33]. These H₂S and sulfides such as pyrite, galena and sphalerite have relatively depleted sulfur isotope compositions, indicating that the sulfate in this gypsum derived from the reoxidation of reduced sulfur (H₂S or pyrite, galena and sphalerite). The oxidation of sulfides occurs mainly by reactions with air oxygen or disproportionation reactions [34,35]. In the former case, the O isotopes of oxygen are about 23.5% heavier than the simultaneous seawater [36], and thus the causative sulfate could show positive O isotope compositions. Therefore, we maintain that this gypsum derived from reoxidation of reduced sulfur by a disproportionation reaction, and the higher Sr isotope composition may be partly inherited from the matrix rock: sandstone.

6.2. The Evolution of the Evaporite Diapirism

The new geochemical data of gypsum and anhydrite allow us to establish a conceptual model modified from Leach et al. (2017) and Song et al. (2020) that can explain the evolution of the evaporite diapirism and the formation of host rocks in Jinding [8,9].

Stage 1: The Paleogene fluvial Yunlong Formation gypsum-bearing sediments were deposited in the Jinding deposit area.

Stage 2: With the initial India–Asia continental collision and regional compression, the evaporite-containing limestone sequence of the Upper Triassic Sanhedong Formation was deformed and migrated along a thrust decollement. Then, these evaporite-bearing limestone fragments were extruded into the fluvial sand system of the Yunlong Formation in the deposit area. One the one side, Member I limestone breccias were formed. Meanwhile, the mixture of limestone clasts with sandy sediments caused the formation of Member II clast-bearing sandstone. During the stage of waning compression, gypsum-bearing sandy sediments were deposited.

Stage 3: The continued compression induced diapirism of the unconsolidated gypsum-bearing sandy sediments, and formed Member III gypsum-bearing complex and Member IV clast-free sandstone. The thrusting of hanging-wall units (inverted sequence of Triassic to Jurassic) covered these diapiric-related rocks and formed the Jinding dome (Figure 10). The late-stage of diapirism of the Upper Triassic Sanhedong Formation evaporite occurred and formed gypsum-bearing mélange after this thrusting. Finally, the post-diapiric Eocene Guolang Formation sandstone was deposited above this mélange and the Jinding dome.

7. Conclusions

• The gypsum and anhydrite in the Jinding deposit are mainly hosted in limestone breccias (Member I), gypsum-bearing complexes (Member III), and red mélange, some occur as veins in clast-free sandstones (Member IV) and fills in vugs of host rock.
• The δ³⁴S, δ¹⁸O and ⁸⁷Sr/⁸⁶Sr ratios of gypsum/anhydrite in limestone breccias and red mélange are close to the S–O–Sr isotopes of the Upper Triassic Sanhedong Formation anhydrite, indicating that these gypsum/anhydrite were derived from the Upper Triassic Sanhedong Formation evaporite, and formed as a result of evaporite diapirism.
• The δ³⁴S, δ¹⁸O and ⁸⁷Sr/⁸⁶Sr ratios of gypsum in gypsum-bearing complex are similar to S–O–Sr isotopes of the Paleocene Yunlong Formation gypsum of the Lanping Basin, suggesting that this gypsum was derived from the Yunlong Formation, and formed as a result of unconsolidated gypsum–sand diapirism.
• The vein gypsum in clast-free pillow-shaped mineralized sandstone and gypsum in vugs of host rock displayed depleted sulfur and oxygen isotope composition, and formed after supergene minerals such as smithsonite. These gypsum are of supergene origin and the sulfate in them is derived from the reoxidation of reduced sulfur.
• The genetic interpretation of the gypsum/anhydrite in the Jinding deposit further supports that the Jinding dome and associated rocks are related to evaporite diapirism, where evaporites were derived from both the Late Triassic and Paleocene sequences.