Pyrite Veins Research Articles

Mineralization Age and Hydrothermal Evolution of the Fukeshan Cu (Mo) Deposit in the Northern Great Xing’an Range, Northeast China: Evidence from Fluid Inclusions, H–O–S–Pb Isotopes, and Re–Os Geochronology

The Fukeshan Cu (Mo) deposit is a newfound porphyry deposit in the northern Great Xing’an Range (GXR), northeast China. In this paper, we present results of chalcopyrite Re–Os geochronology, microthermometry of the fluid inclusions (FIs), and isotopic (H–O–S–Pb) compositions of the Fukeshan Cu (Mo) deposit. Its ore-forming process can be divided into sulfide-barren quartz veins (A vein; stage I), quartz + chalcopyrite + pyrite veins (B vein; stage II), quartz + polymetallic sulfide veins (D vein; stage III), and barren quartz + carbonate ± pyrite veins (E vein; stage IV), with Cu mineralization mainly occurred in stage II. Three types of FIs are identified in this deposit: liquid-rich two-phase (L-type) FIs, vapor-rich two-phase (V-type) FIs, daughter mineral-bearing three-phase (S-type) FIs. The homogenization temperatures of primary FIs hosted in quartz of stages I–IV are 381–494 °C, 282–398 °C, 233–340 °C, and 144–239 °C, with salinities of 7.2–58.6, 4.8–9.9, 1.4–7.9, and 0.9–3.9 wt. % NaCl equivalent, respectively. FIs microthermometry and H–O isotope data suggest that the ore-forming fluids were magmatic in origin and were gradually mixed with meteoric water from stages II to IV. Sulfur and lead isotope results indicate that the ore-forming materials of the Fukeshan Cu (Mo) deposit were likely to have originated from Late Jurassic intrusive rocks. The available data suggest that fluid cooling and incursions of meteoric water into the magmatic fluids were two important factors for Cu precipitation in the Fukeshan Cu (Mo) deposit. Chalcopyrite Re–Os dating yielded an isochron age of 144.7 ± 5.4 Ma, which is similar to the zircon U–Pb age of the quartz diorite porphyry, indicating that Late Jurassic quartz diorite porphyry and Cu mineralization occurred contemporaneously.

Geochemical characteristics of pyrite in the Dabaozhuang deposit in the Middle-Lower Yangtze River Metallogenic Belt, Eastern China

Dabaozhuang is a pyrite deposit in the Luzong Volcanic Basin, Eastern China, and has similar exhalation-sedimentary features to volcanic massive sulfide deposits (VMS), which commonly form in seawater. To better understand the ore-forming process of this special type of deposit, we employed SHRIMP-SI and LA-ICP MS to measure sulfur isotope and trace element compositions of anhydrite and four types of pyrite from the Dabaozhuang deposit. SHRIMP in situ sulfur isotope analysis indicates a narrow range in δ34S of anhydrite, 21.0–21.7‰, and variable ranges for pyrite, 9.9–10.7‰, for pyrite vein in the deep (Py I); −9.2 to 2.0‰, for cyclic annular and oval-shaped pyrite in massive ore (Py II); 3.1–5.3‰, for massive or disseminated pyrite in the footwall tuff and hematite (Py III); and −29.7 to 30.4‰, for euhedral and coarse pyrite in the carbonate cement (Py IV). δ33S and δ36S in four types of pyrite have no abnormal values, indicating that sulfur isotope fractionation is mainly controlled by thermochemical sulfate reduction (TSR). The higher δ34S values in type I pyrite and anhydrite indicate a mixing process of magmatic fluid and evaporates at depth. Py II and IV have negative δ34S data, indicating the formation temperature of pyrite decreases because of the mixing of lake water. δ34S values in Py III are close to magmatic sulfur, which shows the igneous sulfur (tuff) is an important sulfur source for the disseminated mineralization. Cobalt and Ni content also show that the formation temperature of Py I is highest, and Py IV is lowest. This research indicates that the “VMS-like” deposits could be formed in continental volcanic lakes and are genetically related to SO42−-rich IOA (iron oxide-apatite) deposits.

Origin and evolution of ore-forming fluids of the Larong W-(Mo) deposit, eastern Tibet: Constraints from fluid inclusions, H-O isotopes, and scheelite geochemistry

The Larong porphyry W-(Mo) deposit, formed in the main collisional orogenic stage of Lhasa and Qiangtang terranes, is the first-discovered giant W-(Mo) deposit in the Leiwuqi-Zogang metallogenic belt, Sanjiang region. The W-Mo mineralization occurs as veins and stock-works mainly hosted in the granodiorite porphyry, monzogranite porphyry, biotite granite porphyry, and surrounding schist. Four types of fluid inclusions (FIs) including PC-type (pure vapor CO2), C-type (CO2-H2O), W-type (aqueous two-phase) and L-type (pure liquid H2O) FIs have been identified from Stage I quartz-scheelite ± alkaline feldspar veins, Stage II (including three sub-stages) quartz-molybdenite ± pyrite ± chalcopyrite veins, and Stage III quartz ± calcite ± pyrite veins. The total homogenization temperatures of FIs vary widely (187–437 °C) with multiple peaks, indicating multistage fluid activities. The ore-forming fluids of the main mineralization stages are characterized by CO2 enrichment, high-medium temperature (~270–440 °C), and medium–low salinity (2.4–14.4 wt% NaCl equiv.). The homogenization temperature of W-type inclusions is obviously higher than that of C-type inclusions, and the salinity is relatively lower, implying multiple immiscibility of fluids with continuous escape of CO2. H-O isotopic compositions suggest that the primary ore-forming fluids dominantly originated from magma water. Mo concentrations and δEu values in scheelite indicate a decreasing trend of redox state of ore fluids. From Stage I to Stage II to Stage III, the relatively higher-temperature, CO2-rich, and oxidized fluids gradually evolved into relatively lower-temperature, CO2-poor, and reduced fluids. Here we propose that the decrease of temperature and oxygen fugacity and increase of S2- activity and PH values of the ore fluids caused by continuous fluid-rock interaction and loss of CO2 could account for the successive mineralization of W and Mo at the Larong deposit.

Transport and Evolution of Supercritical Fluids During the Formation of the Erdenet Cu–Mo Deposit, Mongolia

Petrological and fluid inclusion data were used to characterize multiple generations of veins within the Erdenet Cu–Mo deposit, Mongolia, and constrain the evolution of fluids within the magmatic–hydrothermal system. Three types of veins are present (from early to late): quartz–molybdenite, quartz–pyrite, and quartz. The host rock was emplaced at temperatures of 700–750 °C, the first quartz was precipitated from magma-derived supercritical fluids at 650–700 °C, quartz–molybdenite and quartz–pyrite veins were formed at ~600 °C, and the quartz veins were precipitated in response to retrograde silica solubility caused by decreasing temperatures at <500 °C. We infer that over-pressured fluid beneath the cupola caused localized fluid injection, or that accumulated stress caused ruptures and earthquakes related to sector collapse; these events disrupted impermeable layers and allowed fluids to percolate through weakened zones.

The Middle Permian Hongshanliang Manto-type copper deposit in the East Tianshan: Constraints from geology, geochronology, fluid inclusions and H–O–S isotopes

The Hongshanliang copper deposit, hosted in the tuff of the Lower Carboniferous Yamansu Formation, is a typical copper deposit in the Aqishan–Yamansu belt, East Tianshan. Based on crosscutting relationships of veins, textural relationships and mineral assemblages, five alteration/mineralization stages at Hongshanliang have been established: chlorite–sulfide stage (Stage I), quartz–pyrite stage (Stage II), quartz–polymetallic sulfide stage (Stage III), late veins (Stage IV) and supergene process (Stage V).Stage I has mineral assemblage of chlorite–pyrite ± chalcopyrite ± quartz ± sericite, and is commonly characterized by euhedral pyrite with silicates (e.g., chlorite, quartz and sericite) and/or chalcopyrite as its pressure shadow, indicating an early mineralization event with apparent deformation. Stage II is characterized by quartz–pyrite ± chalcopyrite or locally quartz ± gypsum ± anhydrite ± pyrite veins cutting Stage I chlorite–pyrite. The main mineralization stage (Stage III) at Hongshanliang has typical mineral assemblages of quartz–chalcopyrite ± chlorite ± calcite ± sericite, quartz–chalcopyrite–sphalerite–galena ± pyrite and quartz–sphalerite–galena ± chlorite, with veins, veinlets, disseminations and local massive ore types, similar to Manto-type copper deposits regarding mineralization and ore structures. Detailed fluid inclusion study shows temperature of fluids decreased from Stage II (307–484 °C) through Stage III (peak at 160–180 °C, consistent with quartz–chlorite oxygen isotope geothermometer of 190 °C) to Stage IV (129–169 °C), with corresponding salinities of 2.7–26.2 wt% NaCl equiv. (peak at 8 wt%), 2.1–12.3 wt% NaCl equiv. (peak at 8 wt%) and 0.5–7.7 wt% NaCl equiv. (peaks at 4–6 wt%), respectively, indicating an evolved hydrothermal ore-forming system. Such fluid evolution can also be supported by H–O isotopes during water–rock reaction from Stage II (δ18Ofluid = 6.3–8.3‰ and δDfluid = −77‰ to −64‰) through Stage III (δ18Ofluid = − 1.7‰ to 7.0‰ and δDfluid = − 82‰ to − 58‰) to Stage IV (δ18Ofluid = − 2.5‰ to − 2.1‰ and δDfluid = − 77‰ to − 73‰) with a magmatic–hydrothermal origin. Furthermore, sulfur isotopes suggest that fluids of the two mineralization stages (Stage I and III) are predominantly magmatic–hydrothermal, with other influx contribution into the ore-forming system, i.e., minor Early Carboniferous seawater in Stage I (δ34Sfluid varying from − 3.5‰ to 6.1‰, with peak at 0‰) and minor organic materials in Stage III (δ34Sfluid varying from − 6.5‰ to 4.1‰, with peak at 0–1‰, and detection of CH4 and C2H6 from fluid inclusions).In combination of alteration, paragenesis, nature and source of ore-forming fluids and comparison with other typical deposits, we proposed that the Hongshanliang copper deposit underwent two mineralization events with the main mineralization similar to Manto-type copper deposits. 40Ar/39Ar dating of sericite from a massive chalcopyrite ore indicates the Hongshanliang main mineralization formed at 269.0 ± 0.4 Ma, generally coeval with regional K-feldspar granite emplacement (ca. 272 Ma). Integrating the regional tectonic setting, magmatism and metallogenesis of the Aqishan–Yamansu belt and the East Tianshan, we suggest that the Aqishan–Yamansu belt has potential of mineral prospecting for the Middle Permian Manto-type copper deposits.

Geology of the Souter Head subvolcanic complex, Aberdeenshire, Scotland: an Ordovician granite-related Mo–(Bi–As–Au) system

ABSTRACTAn Ordovician subvolcanic intrusive complex hosted by Neoproterozoic metasediments crops out at Souter Head about 6km S of Aberdeen, Scotland. The complex is composed mainly of two-mica red granite and breccia with minor dykes of pegmatite, quartz porphyry, felsite and dolerite, and widespread quartz veining, hydrothermal alteration and minor molybdenite mineralisation. Anomalous levels of bismuth (Bi), arsenic (As) and gold (Au) occur in quartz–pyrite veins. The complex has been mapped and the major- and minor-element geochemistry, including rare-earth elements of intrusives and mineralisation, has been determined. These data reveal a complex tectonic, intrusive and hydrothermal history. The intrusives are peraluminous and magnetite-, muscovite- and garnet-bearing. The youngest member, a quartz porphyry, is highly fractionated. There are two stages of hydrothermal activity: the first is linked to the explosive release of volatiles from a granite cupola and breccia formation; and the second, widespread quartz veining. Mo is associated with both stages, and Bi–As–Au anomalies are found in late quartz–pyrite veins. The mineralisation is classified as a granite-related vein-type Mo system. The unique preservation, in the Grampian terrane, of an Ordovician subvolcanic complex may be attributed to pre-Devonian movements on the nearby Dee fault and possibly also the collapse of the magma chamber following the explosive release of volatiles. The combination of large size, poor exposure and abundant multi-stage hydrothermal activity suggests that there is potential for further Mo and possibly Au mineralisation in this complex. Further mineralisation of this style may be present in the NE Grampian terrane.

The 127 Ma gold mineralization in the Wulong deposit, Liaodong Peninsula, China: Constraints from molybdenite Re-Os, monazite U-Th-Pb, and zircon U-Pb geochronology

The Wulong deposit is a large tonnage deposit (>80 t of Au), characterized by quartz vein style of gold mineralization in the Liaodong Peninsula, China. The auriferous quartz veins are mainly hosted by Late Jurassic gneissic two-mica granite (165–157 Ma) and Early Cretaceous granodiorite (129 Ma) and are structurally controlled by NNE- and NW-trending faults. Previous attempts to date the gold mineralization yielded ambiguous results (135–112 Ma). Here we report the first in-situ and direct age constraint for gold mineralization at Wulong. Five molybdenite samples from Mo-bearing quartz ± pyrite veins yielded an isochron age of 127.6 ± 2.3 Ma. In-situ SIMS U-Th-Pb dating of hydrothermal monazite that coexists with gold-bearing pyrite and quartz yielded a 208Pb-232Th age of 126.7 ± 3.2 Ma. These robust ages, together with new age data of the Wulong host intrusion and post-ore dike, allow for a better interpretation of the ore genesis of the Wulong deposit relative to a well constrained sequence of regional geological events. Zircon U-Pb dating of the Wulong host intrusion (gneissic two-mica granite), representing the oldest magmatic event at Wulong, gave a weighted mean age of 159.3 ± 1.4 Ma that is interpreted to be the magma emplacement age. Subsequent magmatic events are recorded by the Early Cretaceous dikes with zircon U-Pb ages between 127 and 113 Ma. A post-ore diorite porphyry dike that crosscuts the Early Cretaceous dikes has a U-Pb zircon age of 121.5 ± 1.5 Ma. All the lines of geochronology evidence suggest a distinct genetic link between the gold mineralization and the Early Cretaceous magmatism in the Wulong orefield. This episode of magmatism and mineralization corresponds to the lithospheric thinning within the northeastern North China Craton, which is triggered by the subduction of the Paleo-Pacific plate.

The nature and age of Mesoproterozoic strike-slip faulting based on Re–Os geochronology of syntectonic copper mineralization, Assynt Terrane, NW Scotland

In ancient basement regions such as the Lewisian Complex, NW Scotland, the ages of brittle deformation events are commonly poorly constrained owing to a lack of datable fills. An array of NW–SE sinistral and antithetic east–west dextral faults related to a regionally recognized episode of brittle shearing cut Neoarchean gneisses and c. 2.25 Ga quartz–pyrite veins close to the trace of an unexposed, regional-scale NW–SE fault. Copper–iron mineralization occurs at an intersection between an antithetic dextral fault and an older c. 2.25 Ga quartz vein. Optical microscopy, SEM and XRD analyses reveal an array of intergrown, co-genetic copper–iron sulfides, hematite and barite. Complex millimetre-thick zoned alteration rims rich in epidote occur at contacts between the sulfides and gneisses. Rhenium–osmium copper–iron sulfide geochronology yields an age of c . 1.55 Ga for the hydrothermal mineralization event associated with faulting. Fault movements demonstrably overlap with mineralization based on the asymmetric fibrous growth forms of these minerals within local dextral shears, which acted as local channelways for mineralizing fluids during and after faulting. We tentatively propose that this regionally recognized strike-slip faulting, previously termed the ‘Late Laxfordian’, should be referred to as the ‘Assyntian’ to distinguish it from kinematically distinct Laxfordian events.

Geology, mineralogy and geochemistry of the Shangxu orogenic gold deposit, central Tibet, China: Implications for mineral exploration

Shangxu is an orogenic gold deposit within the Bangong-Nujiang suture zone, central Tibet, China. It is hosted by turbidite sedimentary rocks of the Jurassic Mugagangri Group. The host rocks were metamorphosed to subgreenschist facies prior to being hydrothermally altered adjacent to mineralization. Hydrothermal minerals in wall rocks consist of muscovite, carbonate, sulfides and chlorite. Whole rock geochemistry indicates hydrothermal alteration is characterized by the introduction of K2O, CO2 and S, and leaching of Na2O. Increasing 3 K/Al and decreasing Na/Al alteration indexes approaching the ore correlate to muscovitization. CO2 concentration reflects the degree of carbonation, which in conjunction with molar (Mn + Fe)/(Fe + Ca + Mg + Mn) and CO2/CaO can be used to distinguish siderite from ankerite in carbonate alteration. Mass transfer analysis shows gains in As, Au, CO2, W, Ca, Cd, Ni, Cr, Sr, Rb, K and losses in Na, Pb, Cu during hydrothermal alteration. In the muscovite alteration zone, muscovite within shear zones (Ms1) shows an increase in Fe, Mg and Na towards the ore, whereas metamorphic muscovite along cleavage planes and in pressure shadows (Ms2), and hydrothermal muscovite (Ms3) change in composition from phengitic (Mg, Fe) distal to mineralization, to paragonitic (Na) adjacent to gold. In carbonate alteration, the composition in carbonate phases changes from early magnesian siderite to ankerite, and then to calcite and dolomite during the evolution of the hydrothermal system. Siderite spots in host rocks and ankerite in veins, wall rock or its replacement of siderite are all enriched in Fe, Mn and depleted in Mg from proximal to distal alteration zones. Pyrite is a dominant mineral in sulfide alteration of the Shangxu deposit. The earliest framboidal pyrite (Py1) formed during diagenesis, and overprinted by Py2, which is recrystallized pyrite associated with burial metamorphism. Py3 rims and enlarges previous pyrite aggregates, or recrystallizes into cubic grains with cracks and quartz pressure shadows during deformation. Py4 is ore-related euhedral pyrite, disseminated near gold, and formed in hydrothermal stage. Vein pyrite (Py5) coexists with marcasite, and fills cracks in quartz veins. Hydrothermal alteration minerals form overlapping alteration haloes surrounding the main auriferous lodes. Distal muscovitization, carbonatization and proximal sulfidation constitute a progressive alteration front from gold. The alteration envelope is tabular in shape, following the strike and dip of the mineralization, and tends to be the widest around the thickest parts of the ore, such that the occurrence and thickness of the alteration envelope can be used as an approximate guide to the size of gold mineralization. Shangxu shares many diagnostic features with turbidite-hosted orogenic gold deposits, such as Bendigo, Reefton and Meguma districts, in deposit geology, alteration mineralogy and lithogeochemistry.

Fluid Inclusion Characteristics of the Kışladağ Porphyry Au Deposit, Western Turkey

The deposit occurs in a mid-Miocene monzonite magmatic complex represented by three different intrusions, namely Intrusion 1 (INT#1), Intrusion 2 (INT#2, INT #2A), and Intrusion 3 (INT#3). Gold mineralization is hosted in all intrusions, but INT#1 is the best mineralized body followed by INT#2. SEM-CL imaging has identified two different veins (V1 and V2) and four distinct generations of quartz formation in the different intrusions. These are: (i) CL-light gray, mosaic-equigranular quartz (Q1), (ii) CL-gray or CL-bright quartz (Q2) that dissolved and was overgrown on Q1, (iii) CL-dark and CL-gray growth zoned quartz (Q3), and (iv) CL-dark or CL-gray micro-fracture quartz fillings (Q4). Fluid inclusion studies show that the gold-hosted early phase Q1 quartz of V1 and V2 veins in INT#1 and INT#2 was precipitated at high temperatures (between 424 and 594 °C). The coexisting and similar ranges of Th values of vapor-rich (low salinity, from 1% to 7% NaCl equiv.) and halite-bearing (high salinity: >30% NaCl) fluid inclusions in Q1 indicates that the magmatic fluid had separated into vapor and high salinity liquid along the appropriate isotherm. Fluid inclusions in Q2 quartz in INT#1 and INT#2 were trapped at lower temperatures between 303 and 380 °C and had lower salinities between 3% and 20% NaCl equiv. The zoned Q3 quartz accompanied by pyrite in V2 veins of both INT#2 and INT#3 precipitated at temperatures between 310 and 373 °C with a salinity range from 5.4% to 10% NaCl eq. The latest generation of fracture filling Q4 quartz, cuts the earlier generations with fluid inclusion Th temperature range from 257 to 333 °C and salinity range from 3% to 12.5% NaCl equiv. The low salinity and low formation temperature of Q4 may be due to the mixing of meteoric water with the hydrothermal system, or late-stage epithermal overprinting. The separation of the magmatic fluid into vapor and aqueous saline pairs in the Q1 quartz of the V1 vein of the INT#1 and INT#2 and CO2-poor fluids indicates the shallow formation of the Kışladağ porphyry gold deposit.

Fluid inclusion and H–O isotope study of the Jiguanshan porphyry Mo deposit, Xilamulun Metallogenic Belt: implications for characteristics and evolution of ore-forming fluids

We studied the fluid inclusions of the Jiguanshan Mo deposit in China, which is a large porphyry deposit located in the southern Xilamulun Metallogenic Belt. The irregular Mo ore body with various types of hydrothermal veinlets is hosted by Late Jurassic granite porphyry. Intense hydrothermal alterations in the deposit from the core to margin are silicification–potassium feldspar alteration, pyrite–quartz–sericite–fluorite alteration, and propylitic alteration. Based on the mineral assemblages and crosscutting relationships of ore veins, the ore-forming process were divided into three stages and two substages: quartz–pyrite veins (stage I) associated with potassic alteration; quartz–molybdenite–chalcopyrite–pyrite veins (substage II-1) and quartz–molybdenite–fluorite veins (substage II-2) associated with phyllic alteration; and fluorite–quartz–carbonate veins (stage III) with carbonation. Five major fluid inclusions (FIs) types were distinguished in the quartz associated with oxide and sulfide minerals, i.e. polyphase brine (Pb-type), opaque-bearing brine (Ob-type), solid halite (S-type), two-phase aqueous (A-type), and vapor (V-type) inclusions. The FIs of stage I were composed of liquid-rich S-, A-, and V-type FIs with homogenization temperatures and salinities of 490 to 511 °C and 8.9 to 56.0 wt% NaCl equiv., respectively. The FIs of substage II-1 are composed of Pb-, Ob-, S-, A-, and V-type FIs with homogenization temperatures and salinities of 352 to 460 °C and 3.7 to 46.1 wt% NaCl equiv, respectively. The FIs of substage II-2 are Ob-, S-, A-, and V-type FIs with homogenization temperatures and salinities of 234 to 309 °C and 3.7 to 39.2 wt% NaCl equiv, respectively. The FIs of stage III are A-type FIs with homogenization temperatures and salinities of 136 to 172 °C and 1.1 to 8.9 wt% NaCl equiv, respectively. Fluid boiling, which resulted in the precipitation of sulfides, occurred in stages I and II. The initial ore-forming fluids of the Jiguanshan deposit had high temperature, high salinity, and belonged to an F-rich NaCl ± KCl–H2O system. The fluids gradually evolved to low temperature, low salinity, and belonged to a NaCl–H2O system. Studies of the hydrogen and oxygen isotope compositions of quartz (δ18OH2O = − 7.3 to 6.3‰, δDH2O = − 104.3 to − 83.3‰) show that the ore-forming fluids gradually evolved from magmatic water to meteoric water.

Geochronology, isotopic chemistry, and gold mineralization of the black slate-hosted Haoyaoerhudong gold deposit, northern North China Craton

The Haoyaoerhudong gold deposit is the largest gold deposit in the north margin of the North China Craton gold province, and contains over 7 Moz of gold at an average grade of 0.62 g/t. The deposit is hosted in the carbonaceous and pyritic slate, phyllite, and schist and is controlled by a tight syncline and shear zones. The high-grade orebodies contains abundant pyrite veins and pyrite-quartz veins. Three stages of pyrite have been identified, including the diagenetic disseminated pyrite, pyrite veins caused by peak matamorphism, and pyrite-quartz veins forming during post-peak metamorphism. Native gold has been observed in pyrite veins and pyrite-quartz veins.The 40Ar/39Ar plateau age of a biotite separate from a tails of boudinaged pyrite-quartz veins is 260.1 ± 2.9 Ma. Combined with previously published 40Ar/39Ar mica age data and low closure temperature of mica, these results suggest that pyrite veins and pyrite-quartz veins were formed during the peak, to post-peak metamorphism during 285–260 Ma, respectively. The lower limit of the formation age of sedimentary disseminated pyrites has constrained to 1670–1560 Ma by the intruded mafic–ultramafic dikes.Disseminated pyrite separates have δ34S values ranging from −39.40‰ to + 17.85‰, 206Pb/204Pb of 19.144–21.892, 207Pb/204Pb of 15.681–15.864, and 208Pb/204Pb of 37.502–38.925, suggesting they were formed from seawater sulfate and has experienced strong sulfur isotopic fractionation. In contrast, hydrothermal pyrites from pyrite veins and pyrite-quartz veins have δ34S values ranging from +6.8‰ to +16.47‰, 206Pb/204Pb of 18.566–18.922, 207Pb/204Pb of 15.645–15.684, and 208Pb/204Pb of 38.924–38.983, which may reflect dissolution-reprecipitation of disseminated sulfides from the pre-existing organic-rich sediments. The mineral paragenetic, geometric, and cross-cutting relationships of pyrite veins and pyrite-quartz veins at Haoyaoerhudong suggest that gold was most likely introduced into pyrite, accompanying sedimentation of the organic-rich shales, and then became enriched during diagenesis. Subsequently, the hydrothermal fluids following metamorphism and shear zone activity make dissolution of the gold in the diagenetic pyrite and precipitated in the intersection of shear zone and tight syncline.

New Data and Evidence on the Mineralogy and Geochemistry of Wulantuga High-Ge Coal Deposit of Shengli Coalfield, Inner Mongolia, China

The mode of occurrence and origin of highly-enriched trace elements, especially Ge, in Wulantuga high-Ge coal deposit have been widely reported. In this study, coal samples and several coalified trunks embedded within the roof strata are collected, which provides a good opportunity to further confirm if Ge is mainly associated with organic matter. Minerals in coal samples are mainly quartz, kaolinite, montmorillonite, pyrite, and gypsum, along with trace albite, barite, chlorite, and Fe-oxide, while those in coalified trunk samples include melanterite, pyrite, and gypsum, with traces of chlorite and magnesiocopiapite. Germanium, As, W, Sb, Hg, Be, and Cs are enriched in coal samples, and these elements are also enriched in the coalified trunks and roof glutenite. The elevated contents of Ge, As, W, Sb, and Hg were almost exclusively derived from the influx of hydrothermal fluids as evidenced by the presence of pyrite veins and chamosite as well as enhanced elemental associations of Ge-W and As-Sb-Hg in the studied lignite samples. The coalified trunks in the study area should be taken into consideration due to the high contents of hazardous elements that cause potential environmental impacts during mining waste disposal and land reclamation.

Porphyry-related polymetallic Au-Ag vein deposit in the Central City district, Colorado: Mineral paragenesis and pyrite trace element chemistry

The Colorado Mineral Belt is a ~500 km long segment of calc-alkaline to alkaline Laramide-age intrusions and related porphyry and polymetallic vein deposits. The Central City historic Au-Ag mining district in the Front Range of Colorado, USA, has been one of the most productive Au deposits in the Colorado Mineral Belt, with a total of 119.1 t of Au produced between 1859 and 1959. Development of NE-trending Laramide strike-slip faults and re-activation of pre-existing Proterozoic brittle structures in Proterozoic gneiss provided the structural controls for the mineralization of Au and Ag in re-opened pyrite-quartz and base metal veins. Previous studies have related ore formation in the district to the emplacement of Late Cretaceous-Paleogene Laramide porphyritic alkaline intrusions. It remains, however, unclear how to reconcile the Au-Ag enrichment of this deposit with the historic vein descriptions and the evolution of a deep magmatic-hydrothermal porphyry system. Here, we document the crosscutting relationships and the mineral paragenesis of the different vein types and use the trace element chemistry in pyrite to fingerprint Au mineralization and the succession of different veining styles in the Central City district. Based on comparisons to porphyry and polymetallic-style veins worldwide, a revised vein classification is proposed, which distinguishes porphyry, transitional pyrite-quartz, and polymetallic veining styles. These veining styles led to the development of an almost concentric district-wide metal zoning, comprising a central and an intermediate zone, both enriched in Cu-Au-Ag, grading into a peripheral zone enriched in Zn-Pb-Ag. Rare porphyry-style veins include K-feldspar veins and quartz veins with molybdenite ribbons. The transitional-style veins include abundant pyrite-quartz veins that crosscut the earlier formed porphyry-style veins, and disseminated pyrite accompanied by phyllic alteration. Formation of the Au-Ag-bearing polymetallic-style veins was associated with the brecciation and re-opening of pyrite-quartz veins. Based on mineral paragenetic relationships, the polymetallic-style base metal veins can be subdivided into four subtypes, comprising sphalerite-chalcopyrite veins, tetrahedrite veins, enargite-pyrite-quartz veins, and galena-sphalerite-carbonate veins. The textures, mineral inclusions and trace element concentrations in pyrite are distinct for the different vein types and associated alteration halos. Pyrite in pyrite-quartz veins is enriched in Co and Ni, and contains quartz inclusions. In contrast, pyrite in polymetallic base metal veins is characterized by elevated Au (≤20 ppm), Cu, As, Pb, Ag and Sb concentrations, and contains inclusions of electrum and galena. The observed veining styles, paragenetic relationships, and associated pyrite chemistry in the Central City district confirm that ore formation is porphyry-related. The Central City district also shares several similarities with Cordilleran polymetallic-style Cu-Zn-Pb-Ag vein deposits associated with Cu-(Mo) porphyries. However, the high Au and low Cu-(Mo) grades make Central City an example of a newly recognized porphyry-related polymetallic Au-Ag vein deposit type.

Trace element associations in magnetite and hydrothermal pyrite from the Geita Hill gold deposit, Tanzania

Gold mineralization in the Geita Hill deposit is associated with pyrite formed along microfracture networks and sulfidation fronts together with K-feldspar and biotite. The sulfidation fronts are best developed in magnetite-bearing ironstone. The gold is present mainly as electrum and gold tellurides along grain boundaries, and as inclusions in pyrite, quartz, biotite and K-feldspar. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of pyrite and magnetite grains reflect complex fluid-host rock interactions. Magnetite textures and chemistry change with alteration intensity, indicating the progression of the alteration front into the host rock. Pyrite textures are uniform across all rock types and reflect late-tectonic growth linked to multi-staged infiltration of hydrothermal fluids. Trace element distribution patterns in pyrite are locally complex and influenced by host rock chemistry.Gold distribution patterns in pyrite correlate closely with Te, Ag, Bi and Pb, indicating that gold occurs in micro- and nano-inclusions of telluride minerals. This is especially so for gold in quartz veins, whereas gold in ironstone and diorite also occurs as electrum with an average Au/Ag ratio of 0.41. As, Co and Ni in pyrite are lattice bound and occur in high concentrations in ironstone and diorite where they show characteristic growth zoning patterns. Pyrite in quartz veins has As, Co and Ni concentrations that are low and variable. Cr, Cu, Mo, Mn and Zn are present in all rock types in isolated inclusions in pyrite grains, whilst Pb, Bi and Sb occur in more dispersed patches of fine clustered inclusions. The Se content in pyrite is typical for Archean gold deposits, and reflects an average temperature of ~340 °C for the mineralizing fluid. The Co/Ni ratio of pyrite grains varies between 0 and 5.2 in ironstone and diorite, and most likely reflects the equilibration Co/Ni ratio of the host rock. The Co/Ni ratio of pyrite grains in quartz veins varies between 1 and 12, and is consistent with a magmatic-hydrothermal origin for the ore fluid. Trace element distribution patterns in magnetite and pyrite indicate that As, Ni, Co, Cr, Mn and Cu were mostly locally derived, and remobilised into the pyrite during sulfidation of the host rock. The concentrations of these elements are strongly lithologically controlled, and they are not consistently incorporated into the pyrite after initial stages of growth. Au, Ag, Te, Bi and Pb were externally derived, and closely correlate in all varieties of pyrite as well as strongly altered magnetite. The alteration footprint of the Geita Hill deposit is limited in extent, and does not involve As and Sb that are typically enriched in Archaean lode-gold systems. Instead, Te and Bi are most characteristic for the deposit and could be of use as path finder elements together with altered magnetite grains.

Origin and evolution of hydrothermal fluids in the Marshoun epithermal Pb–Zn–Cu (Ag) deposit, Tarom-Hashtjin metallogenic belt, NW Iran

The Marshoun epithermal Pb–Zn–Cu (Ag) deposit is located in the Tarom–Hashtjin metallogenic belt (THMB), northwest Iran. The epithermal base metal veins are mainly hosted in Eocene volcanic and volcaniclastic rocks of the Karaj Formation, and late Eocene pyroxene quartz monzodiorite. The mineralization process can be divided into five stages: (1) quartz-chalcopyrite-pyrite veins and breccias, (2) quartz (calcite)-sphalerite-galena ± chalcopyrite ± pyrite veins and breccias, (3) barren post-ore quartz veinlets, (4) barren post-ore calcite veinlets, and (5) supergene mineral assemblages. The primary metallic minerals are pyrite, chalcopyrite, sphalerite, and galena; gangue minerals are mainly quartz, calcite, sericite, and chlorite. The main wall-rock alteration is silicification, intermediate argillic, carbonate, and propylitic alteration. Microthermometric measurements of primary LV fluid inclusion assemblages in quartz and sphalerite indicate that the veins were mainly formed at temperatures between 173 and 285 °C from fluids with salinities between 3.4 and 6.3 wt% NaCl equiv. Coexisting LV, VL, and V inclusions in quartz and sphalerite provide evidence for boiling in ore-stage breccia and veins. Additionally, the occurrence of bladed calcite as well as plumose and colloform/crustiform banded quartz in the ore zones and the presence of hydrothermal breccias are consistent with boiling. Obtained oxygen and sulfur isotope compositions (δ18Owater = +9.2‰ to +1.5‰; δ34SH2S = –10.0‰ to –5.7‰) indicate there was a major contribution from a magmatic component to metallogenesis. The fluid inclusion and stable isotope data indicate that fluid boiling and mixing facilitated hydrothermal alteration and mineralization at Marshoun. The Marshoun deposit is interpreted as an intermediate-sulfidation style of epithermal mineralization. Our data suggest that the epithermal mineralization in the THMB are related to late Eocene (ca. 36–37 Ma) shallow magmatic–hydrothermal activity. The altered Eocene volcanic-subvolcanic rocks, particularly at the intersection of subvolcanic rocks with faults were the most favorable locus for exploration targeting of epithermal ores at THMB.

Mesozoic porphyry Cu–Au mineralization and associated adakite-like magmatism in the Philippines: insights from the giant Atlas deposit

The Atlas porphyry Cu–Au deposit is located in central Cebu Island in the Philippines, with a proven mineral reserve of 1420 Mt at 0.45% Cu, 0.24 g/t Au, 0.018 g/t Mo, and 1.8 g/t Ag. It is associated with the Lutopan quartz diorite porphyry stock that was emplaced into the Cretaceous volcano-sedimentary sequences of the Cansi Formation. Two stages of hypogene alteration have been identified at Atlas: stage I quartz–magnetite ± chalcopyrite ± pyrite veins associated with potassic and propylitic alteration and stage II anhydrite–pyrite–chalcopyrite ± specularite veins associated with phyllic alteration. Supergene gypsum veins are also present. Mineralization is mainly associated with the stage I and stage II veins. The Lutopan quartz diorite porphyry yielded a zircon U–Pb age of 108.5 ± 1.6 Ma and is characterized by high Sr/Y (54–69), with the corresponding magma having high oxygen fugacity (avg. ΔFMQ +2.7, avg. Ce4+/Ce3+ of zircon = 439) and H2O concentrations (presence of amphibole and biotite phenocrysts) and low magmatic temperatures (avg. Ti-in-zircon thermometry = 706 °C). The relatively low La/Yb ratios (9–11), listric-shaped normalized REE patterns with weak or absent Eu anomalies, together with zircon eHf(t) values of 3.4 to 10.0, whole-rock ISr values of 0.70373–0.70382, eNd(t) values of 2.4–3.4 and Mg numbers of 49–53 suggest that the Lutopan quartz diorite porphyry was likely derived from partial melting of young lower continental crust or interaction between asthenospheric melts and lower crust melts, that evolved to adakite-like trace element compositions through amphibole fractionation. Stage I veins yielded a pyrite Re–Os isochron age of 110.2 ± 5.6 Ma, making Atlas the only Mesozoic porphyry deposit discovered in the Philippines.

Fluid inclusion and stable isotope constraints on ore genesis of the Zajkan epithermal base metal deposit, Tarom–Hashtjin metallogenic belt, NW Iran

In the Zajkan Pb–Zn–Cu (Au–Ag) deposit of the Tarom–Hashtjin metallogenic belt (THMB), northwest Iran, mineralization occurs as quartz-base metal sulfide veins hosted by Eocene volcanic and volcaniclastic rocks of the Karaj Formation. Four stages of ore formation are identified at Zajkan: (1) quartz-chalcopyrite-pyrite veins, (2) quartz-galena-sphalerite ± chalcopyrite ± pyrite veins and breccias, (3) quartz-hematite veins and breccias, and (4) barren quartz-carbonate veinlets. The primary metallic minerals are pyrite, chalcopyrite, sphalerite, galena, and trace amounts of hematite; gangue minerals are mainly quartz, sericite, chlorite, and calcite. The main wall-rock alteration is silicification, and intermediate argillic, and propylitic alteration. The coexistence of different types of fluid inclusions (LV, VL, and V) in individual fluid inclusion assemblages in quartz and sphalerite suggests boiling and heterogeneous trapping. Excluding the heterogeneously entrapped fluid inclusions, the microthermometric measurements of primary LV fluid inclusion assemblages in quartz and sphalerite indicate that the veins were formed at temperatures between 217 and 273 °C from fluids with salinities between 1.7 and 6.4 wt% NaCl equiv. The oxygen isotopic compositions (δ18Owater-VSMOW of +3.7 to +1.1‰) indicate that the ore-forming fluids were mainly derived from magmatic water with the input of meteoric water in the later ore-stages. Sulfur isotopic values of sulfide minerals vary over a narrow range from −5.0 to −0.9‰VCDT (averaging −2.2‰VCDT), suggesting that sulfur was derived from a homogeneous magmatic source. The fluid inclusion and stable isotope data indicate that fluid boiling and mixing facilitated hydrothermal alteration and mineralization at Zajkan. Our data suggest that the Zajkan deposit is an intermediate-sulfidation style epithermal mineralization. The estimated ore formation depth of Zajkan indicates minor denudation in the region and may imply a great prospecting potential for other epithermal mineralization in the THMB.

Metallogenesis and hydrothermal evolution of the Tonggou Cu deposit in the Eastern Tianshan: Evidence from fluid inclusions, H-O-S isotopes, and Re-Os geochronology

The Tonggou Cu polymetallic deposit in the Bogda Orogenic Belt, Eastern Tianshan shows evidence for three stages of hydrothermal mineralization: early pyrite veins (Stage 1), polymetallic sulfide ± epidote–quartz (Stage 2), and late-stage pyrite–calcite veins (Stage 3). Fluid inclusion petrography and microthermometry analyses indicate that the liquid-rich aqueous inclusions (L), vapour-rich aqueous inclusions (V), and NaCl daughter mineral–bearing three phase inclusions (S) formed during the main stage of mineralization, and that the ore fluids represent high-temperature and high-salinity H2O-NaCl hydrothermal fluids that underwent boiling. Stable isotope (H, O) data indicate that the ore fluids of the Tonggou deposit were originally derived from magmatic water in Stage 2 and subsequently mixed with local meteoric water during Stage 3. Sulphur isotope compositions (6.7‰ to 10.9‰) are consistent with the δ34S values of pyrite from the Qijiaojing Formation sandstone, indicating the primary source of the sulphur ore. Furthermore, chalcopyrite grains separated from the chalcopyrite-rich ore samples yield an isochron age of 303 ± 12 Ma (MSWD = 1.2). These results indicate that the Tonggou deposit is a transition between high–sulfidation and porphyry deposits which formed in the Late Carboniferous. It also suggests an increased likelihood for the occurrence of Cu (Au, Mo) in the Bogda Orogenic Belt, especially at locations where the Cu-Zn deposits are thicker; further deep drilling and exploration are encouraged in these areas.

The Anatomy of an Alkalic Porphyry Cu-Au System: Geology and Alteration at Northparkes Mines, New South Wales, Australia

The Late Ordovician-early Silurian (∼455–435 Ma) Northparkes system is a group of silica-saturated, alkalic porphyry deposits and prospects that developed within the Macquarie island arc. The system is host to a spectacular and diverse range of rocks and alteration-mineralization textures that facilitate a detailed understanding of its evolution, in particular the nature and controls of porphyry-related propylitic alteration. The first intrusive phase at Northparkes is a pre- to early-mineralization pluton that underlies all the deposits and varies in composition from a biotite quartz monzonite to alkali feldspar granite. Prior to total crystallization, this pluton was intruded by a more primitive quartz monzonite that marks the onset of a fertile fractionation series. Toward its upper levels, the quartz monzonite is porphyritic and locally rich in Cu sulfides. Subsequently, a complex series of synmineralization quartz monzonite porphyries was emplaced. The quartz monzonite porphyry intrusions have a distinct pipe-like morphology and are ubiquitously K-feldspar–altered with a crystal-crowded porphyritic texture. The textures of the quartz monzonite porphyries and common occurrence of porphyry-cemented contact breccias indicate they were forcibly emplaced and of relatively low viscosity. The quartz monzonite porphyries are therefore interpreted as crystal-bearing, silicate melt-aqueous fluid slurries that represent the conduits through which deep-seated magmatic-derived ore fluid was discharged into the shallow crust (1–2 km depth). Each deposit is centered on a multiphase cluster of quartz monzonite porphyry intrusions that drove discrete hydrothermal systems. Initial fluid evolution was similar in all the deposits, with three major alteration facies developed as largely concentric zones around the quartz monzonite porphyry complexes. The innermost zone is host to Cu sulfide ore and dominated by K-feldspar alteration. This transitions outward through a shell of magnetite ± biotite alteration, with pyrite and minor chalcopyrite, to an outer halo of propylitic alteration. Generally, epidote, chlorite, and pyrite are abundant in the most deposit-proximal propylitic zone, with a decrease in the abundance of pyrite, and then epidote, with increasing distance away from deposit centers. Propylitic alteration, particularly within relatively low permeability rocks, is fracture-controlled and a hierarchy of veins is observed. Veins of chlorite-quartz-pyrite ± calcite ± hematite ± epidote ± chalcopyrite (P1) appear to represent the principal fluid conduits. They are surrounded by pervasive and intense alteration halos with a distinct mineralogical zonation from vein-proximal chlorite-sericite (phengite) ± epidote ± pyrite, through hematite-sericite-chlorite ± epidote, ultimately to a vein-distal hematite-albite ± chlorite ± epidote assemblage. These P1 veins are surrounded by regions in which smaller epidote-chlorite ± calcite ± quartz ± pyrite veins (P2) are abundant, again with zoned alteration envelopes: vein-proximal chlorite-sericite (phengite) ± epidote ± pyrite grades out into an epidote-rich zone, which in turn transitions into vein-distal albite-hematite ± chlorite ± epidote. Areas of weakest propylitic alteration, distant from both P1 and P2 veins, are characterized by small epidote-only veinlets (P3) with albite-hematite halos. Mineralogical transitions across the propylitic zone are therefore repeated in the evolution from P1 to P3 veins, as well as in the halos around these veins. It is the overall vein abundance and overlap of associated alteration halos that controls the intensity and appearance of propylitic alteration in most rocks. Such scale invariance and spatial relationships strongly suggest the transition from P1 to P3 veins reflects a broadly decreasing outward flux of (magmatic-derived?) fluid that passed through the fracture network and progressively reacted with country rocks. Further support for this hypothesis comes from crosscutting relationships and Rb-Sr dating of epidote (returning an age of 450 ± 11 Ma), which demonstrate the bulk of propylitic alteration was coeval with mineralization and potassic alteration. Late-stage fluid evolution at each deposit was unique. Much of the E48 orebody, and locally the GRP314 deposit, was overprinted by texturally destructive, white sericite-albite-quartz-alunite ± chlorite alteration. In the E26 deposit and in regions of the GRP314 deposit a series of quartz-anhydrite ± pyrite ± Cu sulfide veins with distinctive, vein-proximal, sericite-dominant alteration halos cuts the primary, deposit-concentric alteration facies. The vein-distal mineralogy of these alteration halos is controlled by their distance from deposit centers, changing from K-feldspar ± biotite in deposit-proximal veins to chlorite ± epidote-albite in depositdistal veins. Late-mineralization quartz monzonite porphyries at E26 and GRP314 also appear to be related to the generation of anhydrite-quartz ± sphalerite veins and a set of quartz-calcite-pyrite-sphalerite ± chalcopyrite ± galena veins. Postmineralization magmatic activity produced relatively primitive and barren monzonite porphyries and younger alkali basalt dikes.