Stratiform Orebodies Research Articles

Sulfide trace element enrichments in the metamorphic basement-hosted Xinhua Pb-Zn-Cu vein-type deposit, eastern Guizhou province (SW China)

Cambrian carbonate formations are widespread in the western Hunan-eastern Guizhou region (southwestern China), which hosts many Mississippi Valley-Type (MVT) lead–zinc (Pb-Zn) deposits. Regional Pb-Zn mineralization is well developed in the low-grade metamorphic rocks of the basal Proterozoic Banxi Group. The mineralization is associated with quartz veins and generally distributed along NE-trending fault zones. Moreover, these deposits have an extensive distribution and high grade, and are associated with Cu-Ag endowment. However, geological and geochemical research on these Pb-Zn vein-type deposits is relatively limited, and their relationship with the regional MVT mineralization remains unclear. The representative Xinhua deposit in Danzhai district is selected as the study subject. We conducted in situ trace element analyses on the sphalerite and chalcopyrite from the various metallogenic stages, and compared them with published sphalerite trace element data from the MVT Pb-Zn deposits in the western Hunan-eastern Guizhou metallogenic belt. Seven orebodies in Xinhua Pb-Zn deposit have been discovered so far, with a metal resource of over 120,000 metric tonnes of Zn + Pb. Field geology and microscopic petrography have revealed two mineralization stages: An early-stage black sphalerite (Sp-I) followed by reddish-brown sphalerite (Sp-II) mineralization, which corresponds to the main chalcopyrite mineralization stage, and a later-stage light-yellow sphalerite (Sp-III), Cu ore-barren mineralization.LA-ICPMS data indicate that the sphalerite from Xinhua has similar trace element compositions to those from the MVT Pb-Zn deposits in the region. They are relatively enriched in Ga, Cd, and Ge, while depleted in Fe, Co, and Mn. Critical metal Ge and Ga are particularly enriched in sphalerite, especially in Sp-I (Ge max 937 ppm, Ga max 824 ppm). The substitution mechanism of Ge and Ga in sphalerite are likely 2Cu+ + Ge4+ ↔ 3Zn2+ and Cu+ + Ga3+ ↔ 2Zn2+. Indium and Sn are mainly present in Sp-I and Sp-III. Chalcopyrite contains Zn and Sn both exceeding 100 ppm. Contents of Se, Ag, In, and Sn in chalcopyrite are significantly higher than those in sphalerite. Calculation of the sphalerite trace element geothermometer (GGIMFis) suggests that the average sphalerite ore-forming temperatures are 164 °C (Sp-I), 156 °C (Sp-II), and 205 °C (Sp-III), implying medium- to low-temperature mineralization. This indicates a possible influx of high-temperature, in-bearing fluid during the late-stage mineralization.In summary, the faults-controlled vein-type Pb-Zn deposits (e.g., Xinhua) may have been products of the same Kwangsian orogeny as other strata bound MVT deposits, and the Xinhua deposit features two mineralization stages with multiple ore metal sources. During the ore-forming fluid ascent, some ore-forming materials may have precipitated in the fluid conduits. And exposed after the erosion of the shallower stratiform orebodies and strata. Consequently, the Xinhua Pb-Zn deposit represents the preserved ore-fluid conduit phase (in the basement strata) of the MVT mineralization.

Fluctuations of trace elements and Sr isotopes of the multi-stage scheelite in the reduced polymetallic Yupo tungsten skarn deposit, South China: Implications for ore-forming process

The Yupo scheelite (Sch)-bearing deposit is hosted in the external contact zones between the Yupo granodiorite and Cambrian Huangdongkou Formation of South China. The stratiform ore bodies contain hedenbergitic pyroxene (Hd23–69) and andradite-poor garnet (Ad0–22) assemblages, indicating that Yupo is a typical reduced W skarn deposit. The garnet compositions are zoned in a deposit scale inwardly from the periphery of the grossular-rich skarn reaction front to more subcalcic compositions. Scheelite occurs mainly as disseminated grains in the skarn coeval with retrograde alteration (Sch I) and in quartz veins crosscutting skarns (Sch II-1, -2, and -3). Sch II-1 occurs as cores rimmed by Sch II-2, and Sch II-3 as veinlet cutting both of them. The Sch I and Sch II-3 show weak Eu anomalies different from the pronounced positive Eu anomalies of Sch II-1 and -2. All the scheelite contains low Mo contents (<0.1 wt%), together with the subordinate precipitation of molybdenite, indicating a reduced ore-forming fluid system. The Mo content and Eu anomaly jointly reveal that the reducing condition enhanced from Sch I to Sch II-1 and alleviated from Sch II-1 to Sch II-3. The four scheelite generations show gradually increased initial 87Sr/86Sr ratios from 0.7144 to 0.7242, which are higher than that of the magmatic apatite (0.7082–0.7127) and the carbonate rocks (0.7104–0.7109). The Cambrian carbonaceous shale is a high (87Sr/86Sr)i endmember that interacted with the initial ore-forming fluid; continuing interaction was deemed to enhance the reduction of the ore-forming fluid from Sch I to Sch II-1. Weakening of the intensity of fluid-rock interaction with carbonate rocks during vein-type mineralization caused the (87Sr/86Sr)i values of the scheelite to increase gradually. The input of meteoric water decreased the fluid reduction capability during the formation of Sch II-1 to Sch II-3. Fluid-rock interaction dominated the scheelite mineralization of the reduced W skarn deposit.

In situ illite Rb-Sr dating indicates the coevality of Carlin-type gold deposits inside and around the isolated carbonate platform in western Guangxi, China

The western Guangxi is a crucial component of the Guizhou–Yunnan–Guangxi “Golden Triangle”(hereafter referred to as the Golden Triangle) of South China. The most discovered Carlin-type gold deposits in this region are primarily situated at the periphery of isolated carbonate platforms. The ore bodies are vein-like in form controlled by faults, and the wall rock are Triassic carbonate-bearing terrigenous clastic rocks. Recently, some gold deposits have been discovered in the interior of isolated carbonate platforms. The ore bodies are primarily stratiform hosted in sedimentary unconformities. The mineralized strata span from the Cambrian to the Permian, and the host rock include sandy and muddy dolostones, as well as a combination of sandstone, mudstone, tuff, and chert. The geological and geochemical characteristics suggest that these stratiform deposits in the interior of isolated carbonate platforms share common characteristic with Carlin-type gold deposits in China and USA. However, it remains uncertain whether these deposits are products of the one mineralization system and are coeval with those vein deposits at the periphery of the isolated platforms. To address this question, we conducted geological and isotopic dating studies on the Longhuo gold deposit and the De'e gold occurrence in the interior of isolated platforms. The Longhuo stratiform gold deposit occurs along a parallel unconformity in the Carboniferous/Devonian composed of sandstone, shale, tuff, and chert. Hydrothermal illite, quartz and auriferous pyrite fill along joints and fissures, implying that illite formed during the main ore-forming stage and its age could represent the age of gold mineralization. The stratiform orebodies of De'e gold occurrence are hosted in Cambrian sandy and muddy dolostones. Gold occurs as invisible Au in zoned pyrite and arsenopyrite, with a dominant alteration assemblage of silicification, carbonate alteration, and illitization. Hydrothermal quartz, illite and dolomite often aggregate with zoned auriferous pyrite and arsenopyrite in the most intensely altered zones, suggesting that illite formed during the main ore-forming stage and its age could also represent the age of gold mineralization. Illite LA-ICP-MS Rb-Sr dating was performed on both deposits, yielding ages of 184.16 ± 3.14 Ma for the Longhuo gold deposit and 191.21 ± 6.76 Ma for the De’e gold occurrence.Previous studies have indicated that Carlin-type gold deposits in the Golden Triangle exhibits two distinct age clusters, one ranging from 184 to 235 Ma and the other from 134 to 148.4 Ma. These dual age clusters suggest the potential occurrence of two mineralization events. The obtained ∼ 190 Ma mineralization ages for the Longhuo and De'e gold deposits in this study indicate that the Carlin-type gold mineralization within the isolated platform took place during the Early Jurassic. This aligns with the early mineralization event of gold deposits along the platform's edge, implying that gold deposits inside and around the isolated carbonate platform are products of the same mineralization system, influenced by post-Indosinian extensional events. The interior of the isolated carbonate platform holds substantial exploration potential, making it a novel direction for prospecting Carlin-type gold deposits in western Guangxi.

Devonian stratiform ironstone deposits in South China formed in a shallow marine environment of a passive continental margin

Devonian ironstone deposits in South China are widely distributed and are major Fe resources of China. They are spatially associated with coeval SEDEX sulfide and Mn deposits. Stratiform orebodies of these ironstone deposits are part of the middle and late Devonian shallow marine sedimentary sequences. The main ironstone layers are interlayered with silty or muddy shales and limestones. The majority of these deposits contain hematite ores and some deposits contain siderite ores. Hematite ores display ooidal textures with Fe-rich ooids and they have Hg isotopic compositions indicative of multiple sources of metals, but trace elemental concentrations are supportive of sources of Fe from seafloor hydrothermal fluids. The Devonian ironstone deposits in South China were formed in a passive continental margin under shallow water conditions. These deposits and coeval SEDEX sulfide and Mn deposits were formed in the same continental shelf but in different sub-basins when the South China Block drifted northward after it was separated from Gondwana.

The world-class carbonate-hosted Fankou Zn-Pb deposit in China. Part II. Alterations: C-O isotopic halos footprint the nature and transfer pathway of ore-fluids, and quantitative water-rock interaction process

The giant Fankou Zn-Pb deposit (more than 10 Mt Zn + Pb metals, grading at 15 %), situated in northern margin of the Quren Basin, is one of the largest Zn-Pb deposits in China. The stratiform orebodies are jointly bounded by both the strata (in the specific layers of Middle to Upper Devonian Donggangling and Tianziling carbonate sequences) and the fault system (a three-order thrusting fault system). Ore textures of carbonate dissolution, replacement-infilling and cementation are widespread in Fankou, analogous to a MVT (Mississippi Valley-type) deposit. Owing to the poorly developed fluid inclusions, the nature of the Fankou ore fluids remains indeterminate. To address this problem, we herein utilize micro-petrography, carbon-oxygen (C-O) isotopes and quantitative isotopic exchange modelling to trace the ore-fluids and water-rock interaction process. A total of ninety-three (93) carbonate samples, covering the majorities of stratigraphic horizons, planar locations, and various alteration intensities, were systematically collected. Micro-petrography reveals the primitively sedimentary bioclastic limestone suffer from heterogeneous dolomitization and carbonatization followed by massive Zn-Pb precipitation. These carbonate samples display a widely-ranged, δ18O- and δ13C-depleted isotope signature (δ18O = 12.57 to 23.82 ‰, δ13C = −7.79 to −0.46 ‰), relative to normal marine carbonates (δ18O = 25 ‰, δ13C = 0 ‰). Further modelling of isotopic exchange indicates a low-temperature (100 to 250 °C), δ18O-depleted (−3 to 7 ‰) and δ13C-depleted (−10 to −7‰) ore fluid equilibrated with the host rock by a relatively low water-rock ratio (W/R = 1 to 10). In terms of space, we identified a relatively decreasing trend of δ18O and δ13C isotopic compositions of carbonates, from southeast to northwest, and from bottom to up. Based upon the previous structural analysis, we interpret that the δ18O and δ13C isotopic distribution patterns are caused by a northwestwards transfer pathway of ore-fluids along the thrusting fault system, and the metalliferous, δ18O- and δ13C-depleted fluids are sourced from the interior of the Quren Basin. Collectively, we clarify the deep southeastern part of the Fankou Zn-Pb deposit and the interiors of the Quren Basin is the favorable exploration target in future.

History of the study and the principal features of the MVT-type lead-zinc massive sulfide deposits of the Priargunsk minerogenic zone

Two types of ore deposits are distinguished within the Priargunsk minerogenic zone: the lead-zinc massive sulfide ore deposits in the Vendian-Cambrian carbonate sedimentary rocks (MVT type) and the polymetallic massive sulfide ones in the Mesozoic volcanogenic rocks (VMS type). The MVT-type deposits are confined to the volcanogenic-carbonate–terrigenous formation and comprise two genetic types of the ore bodies, the stratiform (stratified) beds and the stockwork-shaped hydrothermal-metasomatic zones in the feeding channels. The stratiform ore bodies occur concordantly with stratification of the host rocks in gentle paleodepressions; they are confined to the contacts of limestones with dolomites and carbonaceous siltstones or are controlled by interlayer tectonic deformations. Ore deposits of this type formed synchronously with sedimentation. At the same time, the mechanism of formation of stratiform or stratified ore bodies could be fundamentally different.

Multi-Isotopic Compositions of Ores from the Shizishan Cu–Au–Mo Orefield in the Tongling Region, Eastern China: Implications for Ore Genesis

The Middle–Lower Yangtze Metallogenic Belt (MLYMB) hosts abundant porphyry–skarn–stratabound-type Cu–Au–Mo deposits. Despite extensive research, the origin of the stratabound-type deposits, which developed at the unconformity interface between the Devonian and Carboniferous strata in the MLYMB, remains controversial. The primary debate centers on whether these deposits are the result of Carboniferous sedimentary exhalative mineralization or Mesozoic magmatic–hydrothermal mineralization. In this paper, we examine three representative deposits in the Shizishan orefield: the Chaoshan skarn-type Au deposit, the Hucun porphyry–skarn-type Cu–Mo deposit, and the Dongguashan Cu–(Au) deposit, which has a disputed genesis of its stratiform orebodies. Economically important ore minerals, such as chalcopyrite, molybdenite, and pyrrhotite, and their associated quartz and calcite, were focused on, rather than the extensively studied pyrite in the Tongling region. The ore genesis and sources of mineralized elements in the Shizishan orefield were investigated using H, O, C, S, Pb, and Cu isotopes. The H–O isotopic compositions of hydrothermal quartz from the Chaoshan, Dongguashan, and Hucun deposits indicate that the ore-forming fluids were mainly magmatic water with some meteoric water input. The C–O isotopic compositions of calcite show a large difference from the local sedimentary carbonates. The S isotopic compositions of sulfides reveal a magmatic sulfur signature. The Pb isotopic compositions in the three deposits are similar to those of the Shizishan intrusions, suggesting a magmatic source for Pb. The Cu isotopic compositions of chalcopyrite and pyrrhotite demonstrate that Cu, the primary ore-forming element, was mainly derived from magmatic–hydrothermal fluids. The stratiform orebodies display H–O–C–S–Pb–Cu isotopes consistent with the porphyry orebodies in the Dongguashan deposit, as well as in the Chaoshan and Hucun deposits, indicating a common ore genesis. From these, we conclude that the porphyry–skarn–stratabound-type Cu–Au–Mo deposits in the Shizishan orefield can be classified as a unified Mesozoic magmatic–hydrothermal metallogenic system. The stratabound-type copper sulfide deposits and the porphyry–skarn-type copper deposits in the MLYMB have a strong similarity in the source and genesis of their ore-forming elements.

Paleozoic VMS-type stratiform mineralization overprinted by Mesozoic vein-type mineralization in the Yushui copper deposit, eastern Guangdong, South China

The South China hosts a number of stratiform deposit in Late Paleozoic depression, including the Yushui copper deposit (which has a Cu grade up to 53% with an average grade of about 3.5%) in the Yong-Mei-Hui depression. The genesis type of Yushui copper ore is highly controversial due to the influence of post mineralization tectonic and magmatic activities, which affects the exploration of the deposits. Yushui copper deposit is mainly composed of stratiform ore body and stockwork orebody in the footwall, with typical VMS-type deposit characteristics and its mineralization age of 308 Ma. Small amounts of vein-type ore body can also be seen in the hanging wall dolomite of the stratiform ore body, which mainly develops along the joints and faults, and the mineral assemblage includes chalcopyrite, bornite, galena, sphalerite, tetrahedrite, furutobeite, and rare earth minerals (xenotime and bastnaesite). Hydrothermal sericite is also developed when vein-type ore body cut the sandstone in the footwall of stratiform ore body. Pristine euhedral xenotime and bastnaesite crystals from the Yushui Cu mineralized of veins ore body yield LA-ICP-MS weighted mean 206Pb/238U ages of 162.5 ± 6.7 Ma (1 s, MSWD = 11.8) and 164.6 ± 5.3 Ma (1 s, MSWD = 9.5), respectively. Hydrothermal sericite yields a plateau 40Ar–39Ar age of 163.19 ± 7.60 Ma, which is consistent with the xenotime and bastnaesite U–Pb age, suggesting that the vein-type Cu mineralized is generically related to the Middle-Late Jurassic hydrothermal event. These ages indicate that in addition to the major Late Paleozoic mineralization events that formed VMS-type stratiform ore body, there were also small-scale hydrothermal vein-type ore body formed during the Middle and Late Jurassic mineralization events that did not cause major disruptions to the earlier stratiform ore body. Combining with the chronological research of other copper deposits in the southeastern coastal area of China, this article believes that these 170 ∼ 155 Ma deposits were all due to the crust-mantle interaction caused by changes in the subduction angle of the ancient Pacific plate. Our study suggests that the southeastern margin of the South China has potential for the exploration of polymetallic hydrothermal mineralization related to Middle-Late Jurassic magmatic rock.

Garnet U-Pb geochronology and geochemistry reveal deposit types and fluid evolution: An example from the Dongguashan Cu-Au deposit, eastern China

Dongguashan is one of the largest Cu-Au deposits in eastern China, with ubiquitous garnet in the stratiform and skarn orebodies. The stratiform ore-formation remains enigmatic. In this study, we describe the diverse textures and present new U-Pb age and chemical data for the Dongguashan garnet. Garnet in the skarn orebody can be divided into three generations (Grt-1, Grt-2, and Grt-3). Grt-1 and Grt-2 show three zones from core to inner rim to outer rim (a-b-c). Garnet in the stratiform orebody is homogeneous (Grt-s). All garnet types have low MnO, a wide range of Y/Ho ratios, and visible fluid inclusions, indicating that they formed from hydrothermal replacement. Grt-1a, Grt-1b, Grt-2a, Grt-2c, and Grt-3 are oscillatory-zoned, low-Sn, and HREE-rich grandite, which may have formed from reduced HREE-rich fluids. Meanwhile, Grt-1c and Grt-2b are high-Sn, LREE-rich andradite, and may have formed from oxidized LREE-rich fluids. Grt-s is pure, low-Sn, LREE-rich andradite, and that may have formed from oxidized LREE-rich fluids. The Eu behaviors are sensitive to the fluid physicochemical conditions and Cl content. Grt-1, Grt-2, and Grt-s have positive Eu anomalies, and may have formed from acidic and Cl-rich fluids. Grt-3 has negative Eu anomalies and was possibly formed from neutral and Cl-poor fluids. All garnet types at Dongguashan may have formed by infiltration metasomatism in an open system with multiple metasomatic pulses. Grt-1, Grt-2, and Grt-s yielded nearly the same in-situ U-Pb ages of 135.9 ± 2.1 Ma, 135.6 ± 2.2 Ma, and 134.6 ± 1.4 Ma, respectively. We propose that both ore types at Dongguashan deposit are closely related to the Early Cretaceous plutonism.

Two-phase mineralization of Hongtaiping Cu polymetallic deposit in Yanbian area (NE China): Evidence from sulfide Rb–Sr dating and in-situ trace element analysis

The Hongtaiping Cu polymetallic deposit in Yanbian area (NE China) is located in the tectonic junction between the eastern Central Asian Orogenic Belt and the North China Craton. Two mineralization types are identified at the Hongtaiping deposit, i.e., stratiform mineralization hosted in the pyroclastic rocks of the Middle Permian Miaoling Formation (Fm.) and the quartz-sulfide vein-type mineralization controlled by fractures. To determine temporal and genetic relations between the two mineralization types, sulfide Rb–Sr dating and in-situ LA–ICP–MS trace element analysis were conducted. Seven sulfide samples from stratiform orebodies yielded a Rb–Sr isochron age of 268.3 ± 2.6 Ma, which is similar to the reported zircon U–Pb age of ore-hosting pyroclastic rocks of the Miaoling Fm., suggesting that the stratiform mineralization was syngenetic. The initial 87Sr/86Sr ratios of these sulfide samples show value of 0.7102–0.7103 (average of 0.7103), implying a major crustal origin, with certain mantle-derived input, for the ore-forming materials of the stratiform mineralization. Sulfides from the stratiform and vein-type ores have distinct trace elemental features. High Co/Ni ratio and low Se content in pyrite, and high Sn content and low Zn content in chalcopyrite reflect high temperature and vice versa. In the pyrite from stratiform and vein-type ores, average Se contents are 19.72 ppm and 9.70 ppm, and average Co/Ni ratios are 0.20 and 2.46, respectively. Whilst in the chalcopyrite from stratiform and vein-type ores, average Sn contents are 2.49 ppm and 60.31 ppm and average Zn contents are 346.55 ppm and 236.17 ppm, respectively, indicating that the temperature of the stratiform mineralization is lower than that of the vein-type mineralization. Integrating the geological and geochronological features of the two types of mineralization and wall rocks, as well as trace element compositions of the sulfides, we inferred that the stratiform mineralization at the Hongtaiping deposit can be classified as volcanogenic massive sulfide (VMS)-type, associated with the Middle Permian submarine volcanism caused by the subduction of the Paleo-Asian Ocean. The vein-type mineralization was likely related to the Late Triassic felsic magmatism. In a word, two-phase mineralization implies the VMS-hydrothermal reworking-type for the Hongtaiping deposit.

Gold in the Farallones Block of the Shale-Hosted, Clastic-Dominated Castellanos Zinc-Lead Deposit (Northwest Cuba)

The Zn-Pb ores of the Castellanos shale-hosted, clastic-dominated deposit in northwest Cuba average nearly 1 g/t Au, with local maximum concentrations up to 34 g/t Au. This deposit is stratiform with respect to the bedding in the host black shales and shows a bottom to top zoning of ore assemblages made up of a stockwork underlying the main orebody, a basal pyrite-rich zone and a disseminated to massive Zn-Pb ore zone capped by a discontinuous, thin barite-rich zone. Petrographic data and textural relations allow distinguishing five textural types of pyrite (framboidal Py I, colloform Py IIa, euhedral Py IIb, massive Py IIc and banded colloform Py III) successively formed during ore deposition. The main Zn-Pb ore formed after the crystallization of disseminated, sedimentary framboidal pyrite (Py I) in black shales by the superimposition of several crystallization events. The crystallization sequence of the main ore-forming stage evolved from the precipitation of colloform sphalerite and pyrite (Py IIa) with skeletal galena and interstitial dolomite-ankerite to similar ore assemblages but showing subhedral to euhedral crystal habits (Py IIb) and interstitial calcite-rich carbonates. This stage ended with the development of massive pyrite (Py IIc), mainly occurring at the base of the stratiform orebody. A late fracturing stage gave way to the development of a new generation of colloform banded pyrite (Py III) just preceding the crystallization of early barite. Au is mainly concentrated in pyrite showing variable contents in the different textural types of pyrite and a bottom to top enrichment trend. Minimum contents occur in massive pyrite (Py IIc) from the basal pyrite-rich zone (0.18 ppm Au average), increasing in pyrite IIa (from 0.29 to 2.86 ppm Au average) and in euhedral pyrite (Py IIb) (from 0.82 to 9.02 ppm Au average), reaching maxima in colloform banded pyrite (Py III) formed just before the crystallization of early barite at the top of the orebody. Au enrichment in pyrite correlates with that of Sb (0.08–4420 ppm), As (0.7–35,000 ppm), Ag (0.03–1560 ppm) and to a lesser extent Cu (3–25,000 ppm), Ni (0.02–1600 ppm) and Mn (0.6–5030 ppm). Au deposition should have taken place by oxidation and, probably cooling, of reduced (H2S-dominated) fluids buffered by organic matter-rich black shales of the host sedimentary sequence. The input of such reduced fluids in the ore-forming environment most probably occurred alternating with that of the main oxidized fluids which leached Zn and Pb from the large volume of sandstones and siltstones making up the enclosing sequence, thus being responsible for the precipitation of the majority Zn-Pb ore. Supply of Au-carrying reduced fluids might progressively increase over the course of ore formation, reaching a maximum at the beginning of the late fracturing stage. This evolution of Au supply is consistent with the early crystallization of barite since Ba can also only be transported at low temperature by highly reduced fluids. These results highlight the potential of medium-sized, shale-hosted, clastic-dominated deposits to contain economic (by product) Au amounts and show that ore-forming fluids can change from oxidized (SO42+ dominated) to reduced (H2S-dominated), and vice versa, throughout the evolutionary history of a single deposit.

Geology and genesis of the Debao Cu polymetallic skarn deposit, southwestern China

The Debao deposit, with stratiform orebodies in Middle-Upper Cambrian carbonate rocks, is a rare Early Paleozoic skarn copper deposit in the South China Block. Garnet U-Pb dating yielded a lower intercept 206Pb/238U date of 438.8 ± 7.3 Ma, which is coeval with the related granite (439 ~ 441 Ma). Skarns contain garnets with andraditic compositions (Ad53~93Gr4~46Py1~8) and clinopyroxene (Hd5~11Di89~94Jo0~1 and Hd52~85Di13~46Jo1~4) with low Mn/Fe ratios (<0.1), showing typical mineral compositions of Cu skarn deposits. The proximal garnet skarn mainly developed at the bottom and both sides of the orebody, while distal pyroxene skarn developed in its interior and upper parts. The garnets in the bottom of the orebodies contain more andraditic compositions than their upper parts. The prograde skarn minerals have a range of δ18Ofluid values from 8.81 to 9.53‰, and the sulfide minerals of the main ore stage have a range of δ34S values from −2.40 to 2.57‰, both suggesting a magmatic origin of the ores. In the Debao deposit, hydrothermal magnetite from different skarn zones contains substantial amounts of Al, Sn, Ga, Mn, Mg, Ti, Zn, Co, V, and Ni. The content of Al and Ti in the magnetite, which was considered to derive from the wall rock due to fluid-rock interaction, was positively correlated with temperature. Magnetite in the retrograde skarn stage from the proximal garnet skarn zone contains more Ti and V than that from the distal pyroxene skarn zone, indicating a gradual decrease in temperature and increase in oxygen fugacity of the ore-forming fluid in this stage. The magnetite has higher Sn content (mainly hundreds to thousands of ppm) than normal skarn deposits, implying that high oxygen fugacity occurs during the retrograde skarn stage. Subsequently, the formation of magnetite led to a decrease in the oxygen fugacity of the ore-forming fluid. The decrease of oxygen fugacity and temperature provided favorable conditions for subsequent precipitation of Cu sulfides. Minor vein-type Cu mineralization related to late magmatic fluid extraction of sulfur from the sedimentary strata was recognized. All geologic and geochemical data suggested that the deep skarn in the region transformed from Early Paleozoic carbonate has copper mineralization potential.

The Eocene Poshteh Ba–Pb–Zn–Cu deposit, Iran: geological, mineral–chemical, fluid inclusion, and S–O isotopic analysis of a Kuroko-type VMS deposit with paleo-hydrothermal vent chimneys

The Poshteh deposit is the first documented paleo-hydrothermal chimney-bearing volcanogenic massive sulfide (VMS) deposit in Iran. It occurs in the form of well-developed lensoid orebodies within the Eocene volcano-sedimentary sequence, and comprises of laminated, brecciated, banded, massive, and disseminated textures. The stratiform part of this deposit is approximately 500 m long and up to 20 m thick, and consists of massive to semi-massive sulfides and barites, some of which are banded, which are overlain by barite and siliceous exhalites. The stringer zone stratigraphically underlies the stratiform mineralization. Veins within the stringer zone are composed of quartz, barite, pyrite, galena, sphalerite, and chalcopyrite. Three thin layers of exhalative Mn–Fe-bearing chert overlies the sulfide–sulfate orebodies. Four types of fluid inclusions were recognized in barite and quartz encompassing monophase vapor, monophase liquid, two-phase liquid-rich inclusions, and two-phase vapor-rich fluid inclusions. The homogenization temperatures of fluid inclusions mainly vary between 86.2 and 241.9 °C, whereas their salinities focus on 0.99–21.23 wt.% NaCl equiv. The ore-forming fluids of the barite and quartz minerals are characterized by low-to-medium temperature and low-to-medium salinity. The δ34S values of barite associated with the stratiform and stringer barite orebody range from 8.37 to 21.83 ‰, indicating that the sulfur was derived from the seawater. The sulfur isotope values of sulfide (− 5.18 to 9.33 ‰) are similar to those of VMS deposits from other parts of the world. The δ18O data suggest that the ore-forming fluids of the Poshteh deposit were mainly derived from deep subseafloor circulation of seawater. The well-preserved chimneys typically contain distinct concentric outer and inner sulfide- and axial sulfate-rich zones. The outer zones of the chimneys contain mainly pyrite and chalcopyrite. The sulfides within the inner zone consist predominantly of sphalerite, argentite, and galena. The axial conduits are commonly dominated by barite and calcite. The sulfide-rich chimney zones are also characterized by significantly higher metal contents. The presence of paleo-hydrothermal vent chimneys in the Poshteh Kuroko-type deposit and their trace-element contents also provides significant data for understanding the physicochemical conditions of VMS mineralization.

Trace element characteristics of pyrite in Dongguashan Cu (Au) deposit, Tongling region, China

The Dongguashan deposit is the largest and deepest Cu (Au) deposit in the Tongling region, eastern China. The presence of skarn and stratiform ore bodies in the same system of the Dongguashan deposit has caused much debate as to whether the mineralization was associated with magmatic-hydrothermal or sedimentary origin. In this study, in situ (LA-ICP-MS and EPMA) elemental compositions of medium-to coarse-grained euhedral pyrite from the stratiform and skarn ore bodies, and pyritization marble are investigated in the Dongguashan deposit. The results of the studied pyrite samples have relatively consistent trace element composition characteristics and several genetically significant elemental combinations. Gold and Ag are mainly of lattice bound appearance in pyrite. The Pb, Cu, Sb and Tl elements are mainly incorporated into the pyrite structure as substitutions. The distinctly trace element distribution correlations (e.g., Mn, Se and Tl) of the studied pyrites indicate that they were formed in a high temperature and oxidizing environment. Low Au (<0.1 ppm), Cu (mainly <10 ppm), Pb (<10 ppm) and As contents (<100 ppm), relatively low Se content (<50 ppm), and high Co contents, high Co/Ni (mainly >1) and Se/Tl (>10) ratios of the studied pyrites imply that the Dongguashan deposit is most likely to be a magmatic-hydrothermal origin.

Microfabrics, in-situ trace element and sulfur isotope compositions of pyrite from the Jinjiwo copper deposit in Chengmenshan orefield, northern Yangtze Block: Syngenetic stratabound mineralization and hydrothermal remobilization

The Jinjiwo copper deposit is located in the Jiurui ore district of the Middle-Lower Yangtze Metallogenic Belt. The deposit has stratiform orebodies hosted by Late Carboniferous carbonate units. Pyrite is the dominant metallic mineral in the ores. Here we report on an integrated study on the microfabrics, Raman spectroscopy, in-situ LA-(MC-)ICP-MS trace element and sulfur isotope of pyrite, with a view to understand the geochemical variation, genesis of copper mineralization and ore-forming process. Textural observations suggested four types of pyrite corresponding to three metallogenic episodes: syngenetic sedimentation (PyI), metamorphism or deformation (PyII), and skarn-hydrothermal mineralization including the late skarn stage (PyIII) and hydrothermal stage (PyIV). Raman spectra of pyrite reveal subtle differences in band position and widths (FWHM) and display the increasing formation temperature of from PyI, through PyIV and PyIII, to PyII. Colloform and laminated pyrite (PyI) share similarities in behavior of pairs of elements and have low Co/Ni ratios, and the former contains the highest concentrations of Bi, Cu, Pb, Zn, Ag, Au, Mn that suggest rapid precipitation from highly saturated fluids. PyII shows high Co, Ni and As concentrations and Co/Ni ratios of 0.03 to 6.19. PyIII and PyIV have greatly varying Co/Ni ratios of 1.07 to 29 and typically low Au concentrations, suggesting a hydrothermal source. PyIII is rich in Co and Se, but is depleted in As, Cu, Pb, Zn, Ag, and Au in comparison with PyIV. There are two kinds of sulfur: one is that δ34S values are near zero, suggesting that the pyrite sulfur in the ores was derived from a mixed source in deep crust, and the other is that δ34S values are less than −39.1‰, indicating the sedimentary pyrite sulfur was originated from bacterial sulfate reduction. The combined textural and compositional data of pyrite suggest that the formation of the Jinjiwo copper deposit might have recorded the submarine exhalation sedimentation and the Mesozoic tectonic transition-deformation and hydrothermal overprint.

Subaerial explosive deposition of magnetite-apatite mineralization: The Artillero deposit, Peña Colorada district, Colima, Mexico

The Artillero magnetite deposit is a satellite orebody within the Peña Colorada iron district, Mexico. The mineralization consists of a stratiform orebody formed of subaqueous pyroclastic magnetite interbedded with welded rhyodacite. This was likely deposited in a shallow maar crater, capping breccia pipes and feeder dikes, all hosted by coherent Cretaceous rhyodacite. All of these features suggest that this mineralization was formed by the crystallization of iron-rich melts in a subaerial environment. The formation of the magnetite ore in Artillero and Peña Colorada at 90 ± 11 Ma and 81 ± 3 Ma (U-Pb zircon and apatite), respectively, is coeval with the deposition of the rhyodacite host rocks (84 ± 1 Ma; U-Pb zircon). The likely source of the iron-rich melts was the mantle wedge, having a small but noticeable crustal contamination due to the input of fluids derived from dehydrating slab or continental crust incorporated via subduction erosion, which is reflected in an increase in the 87Sr/86Sr values of the Guerrero volcanic arc. Iron-rich melts ascended through strike-slip structures related to compression/extension processes caused by the post-Laramide inversion. The shallow emplacement of the melts favored the separation of large amounts of low-density aqueous fluids, which increased wetting properties of the iron rich magma, favored explosive extrusion, and formed maar-diatreme complexes.

Holocene Boulder Beach Eroded from Chromite and Dunite Sea Cliffs at Støypet on Leka Island (Northern Norway)

This project examines the role of high-latitude storms degrading a Holocene coast formed by igneous rocks composed of low-grade chromite ore and dunite that originated within the Earth’s crust near the upper mantle. Such rocks are dense and rarely exposed at the surface by tectonic events in the reconfiguration of old ocean basins. An unconsolidated boulder beach occupies Støypet valley on Leka Island in northern Norway, formerly an open channel 10,000 years ago when glacial ice was in retreat and rebound of the land surface was about to commence. Sea cliffs exposing a stratiform ore body dissected by fractures was subject to wave erosion that shed large cobbles and small boulders into the channel. Competing mathematical equations are applied to estimate the height of storm waves impacting the channel floor and cliffs, and the results are compared with observations on wave heights generated by recent storms striking the Norwegian coast with the intensity of an orkan (Norwegian for hurricane). Lateral size variations in beach clasts suggest that Holocene storms struck Leka Island from the southwest with wave heights between 5 and 7.5 m based on the largest beach boulders. This result compares favorably with recent high-latitude storm tracks in the Norwegian Sea and their recorded wave heights. The density of low-grade chromite ore (3.32 g/cm3) sampled from the beach deposit exceeds that of rocks like limestone or other igneous rocks such as rhyolite, andesite, and basalt taken into consideration regarding coastal boulder deposits associated with classic hurricanes in more tropical settings.

The Dairi SEDEX Zn + Pb + Ag deposit (North Sumatra, Indonesia): Insights from mineralogy and sulfur isotope systematics

The Dairi Zn + Pb + Ag deposit is the only giant SEDEX deposit that has been discovered to date in Sumatra. Ore-gangue mineralogy and sulfur isotope studies have been carried out to elucidate the paragenetic sequence, deformation of ore, flow direction of ore forming fluid, and sources of sulfur in the Dairi deposit. Stratiform orebodies hosted by the Julu unit (interbedded dolomitic siltstone and carbonaceous shale; multilayers; accounting for greater than 90% of metal resources) consist of pyrite-rich massive, sphalerite-rich massive, bedded sulfide, galena-rich breccias, and vein ore types, whereas discordant orebodies hosted by the Jehe unit (massive and brecciated arenaceous dolostone) comprise vein and disseminated ore types. Fine-grained, subhedral-euhedral and framboidal pyrite (enriched in Co, Ni, Cu, As, Bi, Ag relative to hydrothermal pyrite) were precipitated in the diagenetic stage, followed by precipitation of pyrite (enriched in Zn, Pb, Mn, Tl relative to diagenetic pyrite), sphalerite, galena, chalcopyrite, pyrrhotite, acanthite, tetrahedrite, tennantite, pyrargyrite, boulangerite, freieslebenite, and diaphorite in the hydrothermal stage derived from the exhaled ore-forming fluid. Metamorphic pyrite (enriched in Co and depleted in Cu, Zn, Mn, Tl, Ag relative to the other pyrites) formed from pyrrhotite (depleted in Co relative to metamorphic pyrite) and soft sulfides were remobilized into pyrite fractures and veins during sub-greenschist metamorphism. Ore-forming fluid ascended through fractures in the Jehe unit (forming the discontinuous orebodies) and then it discharged and flowed from SE to NW on the seafloor (forming the stratiform orebodies). Reduced sulfur for diagenetic pyrite (δ34S = -4.1‰ to + 11.6‰) was supplied by bacteriogenic reduction of Carboniferous seawater sulfate. Hydrothermal sulfur was considered as the source of sulfur for the Jehe-hosted orebodies (δ34S = +3.5‰ to + 8.0‰). The heavier δ34S of sulfides in the Julu-hosted orebodies (δ34S = +6.4‰ to + 28.8‰) suggests large-scale bacteriogenic reduction of Carboniferous seawater sulfate in a restricted, anoxic basin. A bacteriogenic reduced sulfur reservoir, rather than hydrothermal sulfur, may be more plausible to account for the scale of the giant Dairi deposit.

Sidi M'Barek: a representative example of the Moroccan massive sulfide deposits

Abstract In addition to a Zn-rich lens representing the northern prolongation of the Draa Sfar volcanogenic massive sulfide deposit, the Sidi M'Barek deposit includes Cu-rich lenses in which gold is being recovered profitably as a by-product. The Cu-rich mineralization is composed of numerous structurally controlled veins whose morphology suits that of a lode rather than that of a stratiform orebody. Although the Cu-rich and Zn-rich orebodies are dominated by pyrrhotite, pyrrhotite is coarser grained in the Cu-rich lenses and mineralization is polyphase. Pyrrhotite is deformed and recrystallized; it is cross-cut and replaced by pyrite infilling veins. Pyrite also crystallizes along the S 1 cleavage and in pressure shadows around bioclasts in the disseminated ore. Chalcopyrite veins postdate both the pyrrhotite and pyrite phases. The concentration of Co and Au is higher in the Cu-rich lenses relative to the Zn-rich lenses, which have higher concentrations of Pb, Ag and As. Pyrite and pyrrhotite have distinct sulfur and lead isotopic signatures. We propose a polygenetic model in which a pre-existing syngenetic pyrrhotite-rich mineralization is remobilized in shear zones during a major ductile deformation event allowing deposition of pyrite. The shear zones were reopened during a late ductile–brittle deformation event allowing deposition of chalcopyrite.

Geological, isotope geochemical and fluid inclusion constraints on the Mishu SEDEX-type Barite (Pb-Cu-Zn) system, NW Iran

The Late Precambrian sedimentary-volcanic sequence of the Kahar Formation at Mishu mountains, NW Iran, hosts the oldest SEDEX-type barite-(Pb-Cu-Zn) mineralization of Iran. These occurrences include Aralan-Pyrbala, Almas, Shanjan, and Daryan that are hosted by organic material-bearing shales, siltstones, and fine-grained sandstones of the Kahar Formation. Based on the morphology of the mineralization and its textures, the mineralization has formed as strata-bound (stockwork zone and massive ore) and stratiform (bedded ore) ore bodies. The stockwork zone consists of an irregular network of vein-veinlets that cross-cut the sedimentary host rocks. The massive ore contains both massive barite and semi-massive sulfide minerals (galena, chalcopyrite, pyrite, and minor sphalerite and tetrahedrite-tennantite). The bedded ore consists of barite-rich layers that are concordant with the bedding of the host rocks. Barite represents the main mineralization at Mishu mountains. Microthermometry on barite minerals from various ore facies (stockwork zone, bedded ore and massive ore), demonstrates that homogenization temperatures (Th L+V) and salinities decrease from the stockwork zone (163 to 285 ℃; and 3.43 to12.40 wt% NaCl equiv.) to the bedded ore facies (142 to 229 ℃; and 3.11 to 8.78 wt% NaCl equiv). The stockwork zone is interpreted to have formed near the paleo-subsurface, and the bedded ore within seafloor sediments. Hence, this trend of the temperatures and salinities probably reflects mixing of cold seawater with hydrothermal fluids, where the seawater proportion is higher in the bedded ore than in the stockwork zone. Based on the homogenization temperatures and salinities of the mineralizing fluids, a buoyancy plume model is proposed as the mechanism for the ore precipitation. The δ34S and δ18O values of barites from the Mishu mineralization range from 34.1 to 41.3‰ and 10.2 to 12.6‰, respectively. These values indicate the influence of seawater. Based on the δ34S versus δ18O diagram, the studied samples are located in the range of cold seeps barite, a term that is commonly used in the literature to describe barite mineralization at continental margins. Sulfur and oxygen isotope composition of barite, along with the sedimentological, textural, mineralogical, and fluid inclusion characteristics, suggest that the Mishu mineralization represents a vent-proximal (Selwyn-type) SEDEX ore deposit.