Quartz-sulfide Veins Research Articles

Mineralization age and geodynamic background for the Shangjiazhuang Mo deposit in the Jiaodong gold province, China

The Shangjiazhuang Mo deposit is located on the Jiaodong Peninsula in eastern China, which is famous for the ca. 120Ma “Jiaodong-type” Au deposits with total Au endowment of over 3000t. In this paper, we discuss the deposit geology, mineralization age, and geochemical features of the host granodiorite of the Shangjiazhuang Mo orebody. Using this information, we aim to clarify the time and geodynamic mechanism for the Mo deposit, which is another constraint to understand the genesis of Au deposits. The Mo mineralization generally occurs as quartz–sulfide veins within the medium-grained Yashan granodiorite. The alteration consists of potassic alteration, silicification, sericitization, chloritization, and carbonatization with a weak unclear zonation. The ore minerals mainly include molybdenite, chalcopyrite, and pyrite. We measured Re–Os isotopes of molybdenite grains, which yielded a weighted mean model age of 116.9±0.81 (MSWD=1.03) and a well-constrained 187Re–187Os isochron age of 117.1±1.4Ma (MSWD=1.6). These ages are slightly younger than the age of Au mineralization on the Jiaodong Peninsula. Rhenium contents of 5.84–29.99ppm with an average of 16.4ppm in molybdenites indicate a crustal source. Whole-rock geochemical compositions show that the granodiorite is high-K calc-alkaline and metaluminous to peraluminous. The samples show low Y contents from 8.2 to 10.5ppm and Sr/Y ratios from 48.2 to 58.8, displaying an adakitic affinity. The Yashan granodiorite has high initial 87Sr/86Sr ratios of 0.7101 to 0.7104, low εNd(t) values of −17.6 to −16.7, and zircon εHf(t) values from −24.8 to −17.1, with corresponding Hf model ages of 2.7 to 2.2Ga. These isotopic data, together with the adakitic affinity of the granodiorite, indicate that the parental magma was derived from ancient crust. Mafic microgranular enclaves (MME) that are contemporaneous with the host granodiorite show SiO2 contents of 57.98–58.41wt% and depletion in Nb–Ta. The MMEs show enriched initial 87Sr/86Sr ratios of 0.7102 to 0.7106 and low εNd(t) values of −17.3 to −16.3. The MMEs are the products of mixing between the metasomatized lithospheric mantle-derived mafic magma and the ancient crust-derived felsic magma. The Early Cretaceous Mo mineralization (120–110Ma) is slightly younger than the peak time of Au mineralization (126–120Ma) on the Jiaodong Peninsula, but have a different spatial distribution which suggests different sources of Au and Mo. The “Jiaodong-type” Au deposits were probably related to the upwelling of metasomatized lithospheric mantle, while the Mo mineralization on the Jiaodong Peninsula may delineate a 120–110Ma Mo metallogenic belt along the southern margin of the North China Craton with the East Qinling, which is related to the melting of ancient crustal sources. The subduction of the Paleo-Pacific slab and accompanying asthenospheric upwelling triggered upwelling of metasomatized lithospheric mantle, forming “Jiaodong-type” Au deposits. Subsequently, the ponding of mantle-derived magmas resulted in partial melting of ancient crust and associated Mo deposits.

Exhaustive gold mineralizing processes of the Sanshandao gold deposit, Jiaodong Peninsula, eastern China: Displayed by hydrothermal alteration modeling

Sanshandao deposit, located in the western end of the Jiaodong Peninsula, is a typical altered-rock type gold deposit. The hydrothermal alteration in the deposit commences from potassic alteration with mineral assemblage mainly composed of K-feldspar and quartz, with minor sericite. The potassic alteration is followed by silicification that is always weakly developed in this district with minor sericite and gold-absent pyrite. As sericite content increases, the silicification alteration is gradually giving its way to sericitization. Fine sulfide crystals occur in this zone scattering in sericite and quartz matrix, which turns to be sulfidation as hydrothermal alteration proceeding. Gold mineralization is mainly associated with the sulfidation, predominantly hosted by pyrite. The latest hydrothermal alteration and veins consist of quartz-calcite-siderite(-ankerite) crosscutting the former alteration zones. Some auriferous sulfide-quartz veins fill the fractures in the alteration zones, but its gold reserve is limited.Geochemical modeling is applied to examine the hydrothermal alteration and gold precipitation processes in the Sanshandao deposit. Modeling shows that a gold-bearing fluid is potential to form an economic gold deposit via various paths, including fluid cooling, water-rock interaction, and fluid mixing with groundwater. The simulation results indicate that the auriferous quartz veins located in the alteration zones are probably generated by fluid cooling and mixing, whereas gold mineralization in the sulfide-sericite alteration stage is primarily caused by water-rock reaction that also produces the hydrothermal alteration following the potassic alteration. To evaluate the roles of water-rock interaction in gold mineralization at different temperatures, we execute simulations at T=400°C and 300°C at pressure of 2kbar. Gold precipitation at >400°C is driven by strong water-rock reaction with low water/rock ratio, during which the gold precipitation is associated with pyrrhotite rather than pyrite, and thus the pyrite at this temperature scale is always gold-absent; at low temperature (∼300°C), the water-rock interaction is effective to precipitate gold from the fluids, and gold mineralization links to pyrite precipitation. The comparison between these two simulations with different temperatures indicates that water-rock interaction at moderate temperature is prior to precipitate gold from hydrothermal fluid, which can be invoked to interpret the fact that gold mineralization is always intense in shallow level and host majority of gold reserve in this deposit. The modeling suggests that pyrrhotite should be paid more attention in future deep exploration since its ability to host certain gold budget at relatively high temperature.

Genesis of the Datuanshan stratabound skarn Cu(–Mo) deposit, Middle–Lower Yangtze Valley, Eastern China: constraints from geology, Re–Os geochronology, mineralogy, and sulfur isotopes

Stratabound deposits are the most abundant and economically significant ore type in the Middle–Lower Yangtze River Valley, one of the most important metallogenic belts in China. The Datuanshan deposit is one of the largest and most representative stratabound Cu(–Mo) deposits in the Tongling district of the Middle–Lower Yangtze River metallogenic belt. All the orebodies of the Datuanshan deposit occur around Mesozoic quartz monzodiorite and are tabular or semi-tabular bodies along bedding-parallel faults within upper Permian to Lower Triassic strata. However, discordant and crosscutting relationships (e.g., the host rocks crosscut by skarn– and quartz–sulfide veins, with alteration halos around the veins) have also been found, especially along the skarn–host contact and orebody–host contact, indicating that skarnitization and mineralization postdated the deposition of the host sediments. The skarn consists mainly of prograde garnet and pyroxene and retrograde alteration assemblages of amphibole, epidote, and chlorite, as well as quartz and sulfides. Electron microprobe analyses show that the garnets and pyroxenes are grossular–andradite and hedenbergite–diopside series, respectively, and all samples plot in the field of typical skarn copper deposits worldwide. Molybdenite samples from stratiform copper ores yield Re–Os model ages of 138.2–139.9 Ma with a weighted mean age of 139.2 ± 0.9 Ma. This is reasonably consistent with the ages of the stratiform Mo ores (138.0–140.8 Ma) and genetically related quartz monzodiorite (135.2–139.3 Ma) in the Datuanshan deposit, indicating that the stratiform Cu and Mo mineralization was contemporaneous with emplacement of the quartz monzodiorite magmas in the Early Cretaceous. Fifteen δ34S values for sulfides range from −1.8 to +4.7 ‰, with a mean of 0.5 ‰, indicating that the sulfur was derived mainly from a magmatic source. Moreover, the sulfur isotope values of the ores are consistent with those of Mesozoic intermediate–acid intrusions but are different from those of sediments in the Shizishan orefield. Based on these lines of evidence, we conclude that the Datuanshan stratabound Cu(–Mo) deposit is the result of replacement related to Mesozoic magmatic rocks and is not a product of submarine exhalative sedimentary processes.

The Relationship between the Structural Orientation and the Gold Mineralisation of Quartz-Sulphide Veins in the Navachab Gold Deposit, Namibia

This study uses a representative dataset of more than 500 vein samples from the Navachab gold deposit containing information on the gold concentration, structural orientation, vein thickness, alteration and host rock type to investigate small scale controls on the grade distribution in the veins in order to obtain a better understanding of the architecture of the Navachab ore bodies. We calculated mean gold concentrations for each vein set in different parts of the mine. We then examine the preferential mineralisation of certain vein sets by setting this grade information into context to other geological parameters such as the structural geology of that particular part of the mine as well as the above mentioned factors structural orientation of the vein, vein thickness, alteration- and host rock type. Our main findings are that vein sets oriented favourably to the stress field and at high angles to the bedding are better mineralised than veins sets oriented at low angles to the bedding. Other factors do not exert a great influence on the gold concentration in the veins. We propose that the gold grade in the veins is influenced by the effectiveness of fluid flow into the veins and by time rates during vein propagation and fluid flow.

Geology and geochemistry of the Huilvshan gold deposit, Xinjiang, China: Implications for mechanism of gold precipitation

The Huilvshan gold deposit in the west Junggar (Xinjiang, China) is hosted in chloritized basalts, chlorite–siderite-altered basalts, and quartz–siderite rocks. Our study demonstrated that all these rocks were derived by alteration of basalts in a shear zone. The orebodies, consisting of quartz-sulfide veins and disseminated sulfides, formed in five stages: quartz–muscovite (I), disseminated sulfides (II), quartz–ankerite-sulfide (III), quartz–calcite-sulfide (IV), and quartz–calcite (V). Auriferous minerals are native gold in stage III and electrum in stage IV. During alteration of basalts in the shear zone, ore-forming elements were released from basalts to ore-forming fluid. Compared with fresh basalts, sulfide-bearing chloritized basalts contain much higher Sr, Ba, P, La, Ce, U, Mn, Ni, Zn, As, Ag, and Au contents. Phase analysis of the As–Cu–Fe–S–O system with the SUPCRT92 software package indicates that a decrease of the aH2S value, caused by the fluid–rock reactions and crystallization of sulfides, induced gold precipitation.

Geology and genesis of the Xiaguan Ag–Pb–Zn orefield in Qinling orogen, Henan province, China: Fluid inclusion and isotope constraints

The Xiaguan Ag–Pb–Zn orefield (Neixiang County, Henan Province), hosting the Yindonggou, Zhouzhuang, Yinhulugou and Laozhuang fault-controlled lode deposits, is situated in the Erlangping Terrane, eastern Qinling Orogen. The quartz-sulfide vein mineralization is dominated by main alteration styles of silicic-, sericite-, carbonate-, chlorite- and sulfide alteration. Major Ag-bearing minerals are freibergite, argentite and native Ag. The deposits were formed by a CO2-rich, mesothermal (ca. 250–320°C), low-density and low salinity (<11wt.% NaCl equiv.), Na+–Cl−-type fluid system. Trapping pressures of the carbonic-type fluid inclusions (FIs) decreased from ca. 280–320MPa in the early mineralization stage to ca. 90–92MPa in the late mineralization stage, indicating that the ore-forming depths had become progressively shallower. This further suggests that the metallogenesis may have occurred in a tectonic transition from compression to extension. Geological- and ore fluid characteristics suggest that the Xiaguan Ag–Pb–Zn orefield belongs to orogenic-type systems.The δ18OH2O values change from the Early (E)-stage (7.8–10.8‰), through Middle (M)-stage (6.0–9.4‰) to Late (L)-stage (−1.5–3.3‰), with δD values changing from E-stage −95 to −46‰, through M-stage −82 to −70‰ to L-stage −95 to −82‰. δ13CCO2 values of the ore fluids in the E- and M-stage quartz vary between 0.1‰ and 0.9‰ (average: 0.3‰); δ13CCO2 values of L-stage FIs are −0.2–0.1‰ in quartz and −6.8‰ to −3.5‰ in calcite. The H–O–C isotopic data indicate that the initial ore fluids were sourced from the underthrusted Qinling Group marine carbonates, and were then interacted with the ore-hosting Erlangping Group metasedimentary rocks. Inflow of circulated meteoric water may have dominated the L-stage fluid evolution.Sulfur (δ34S=1.9–8.1‰) and lead isotopic compositions (206Pb/204Pb=18.202–18.446, 207Pb/204Pb=15.567–15.773 and 208Pb/204Pb=38.491–39.089) of sulfides suggest that the ore-forming materials were mainly sourced from the ore-hosting metasedimentary strata. The stepped heating sericite 40Ar/39Ar detection suggests that the mineralization occurred in the Middle Jurassic to Early Cretaceous (ca. 187−124 Ma). Considering the regional tectonic evolution of the Erlangping Terrane, we propose that the Xiaguan Ag–Pb–Zn orefield was formed in a continent–continent collisional tectonic regime, in accordance with the tectonic model for continental collision, metallogeny and fluid flow (CMF).

Ta Nang gold deposit in the black shales of Central Vietnam

The Ta Nang gold deposit is localized in Middle Jurassic black shales. The ore zone is a series of layer-by-layer crush zones and zones of hydrothermal rock alteration, <10 m in thickness and >2 km in length. It consists of quartz-sulfide veins, sulfidized black shales, and their hydrothermally altered varieties. Sulfide mineralization occurs as two assemblages: early pyrite-arsenopyrite and late chalcopyrite-sphalerite- galena. The pyrite-arsenopyrite assemblage is composed of different morphogenetic varieties. Coarse-crystalline arsenopyrite and pyrite aggregates and metacrystals of different orientations, 0.1 to 10 mm in size, are the most widespread. The chalcopyrite-sphalerite-galena assemblage is scarce. Along with the main ore minerals, it includes more rare minerals: pyrrhotite, lead sulfosalts (tsugaruite), and gold, which form a spatial assemblage with the main minerals or small inclusions in them. Gold occurs mainly as fine dissemination in cracks in pyrite, arsenopyrite, chalcopyrite, and quartz. Gold content in sulfidized carbonaceous shales is no more than tenths of ppm, averaging 0.38 ppm. This content in the quartz veins is considerably higher, averaging 3.92 ppm. Silver contents in the shales and quartz veins are similar and equal to 2.68 and 5.30 ppm, respectively. Also, the sulfidized rocks and veins have elevated contents of Fe, As, Pb, Zn, Cu, Cd, Ni, and Co; most of these elements (Fe, As, Pb, Zn, and Cu) make up their own sulfide minerals, and the others are trace elements. According to 39Ar/40Ar dating of sericite from the quartz-sulfide veins, their age is 129.3 ± 5.6 Ma, which is close to the age of the Cretaceous granite intrusions of the Deo Ca complex. These veins formed from moderately strong solutions (11.7-6.4 wt.% NaCl equiv) with the CH4 + N2 + CO2 gas phase at 340–130 °C. Judging from the S isotope composition (534S = 1.6-4.3%c), predominantly deep-seated endogenic sulfur participated in the formation of ore sulfide associations. Analysis of the distribution of gold shows that it was deposited together with sulfide minerals (galena, sphalerite, and chalcopyrite) at a later stage.

Porphyry Au-Cu mineralization controlled by reactivation of an arc-transverse volcanosedimentary subbasin

Located in the accreted remnants of the Ordovician Macquarie Arc (Australia), Cadia East is the largest alkalic porphyry Au-Cu deposit currently known. The deposit is centered on a 2-km-long, northwest-trending volcanosedimentary subbasin, which was identified by mapping variations in the distribution and thickness of faulted sedimentary marker horizons. The normal faults that define the subbasin predate porphyry mineralization and are oriented parallel to a major arc-transverse lineament. Porphyry Au-Cu mineralization was controlled by reactivation of the subbasin during postorogenic extension as the Macquarie Arc was accreted to the Gondwana margin in the early Silurian. Dilation of the northwest-trending subbasin faults facilitated emplacement of alkalic porphyry dikes and associated sheeted quartz-sulfide veins that define the Cadia East orebody. During the middle Silurian, north-trending fault-bound marine basins buried Cadia East, significantly enhancing preservation of the ore system. These north-trending faults were optimally oriented for reactivation during Devonian east-directed compression, leaving the mineralized Cadia East volcanosedimentary subbasin largely intact. We identify the significance of reactivated premineralization structures within an arc-transverse lineament in controlling porphyry Au-Cu mineralization in a postsubduction setting. At Cadia East, the manifestation of such premineralization structures can be observed at regional, district, and deposit scales, and highlights the influence of preexisting crustal architecture on the structural character, geometry, and preservation potential of porphyry deposits throughout the arc life cycle.

Compositions and Pressure–Temperature Conditions of Metamorphic Fluids Overprinting the Talate VMS Pb–Zn Deposit, Southern Altay, China

The Talate Pb–Zn deposit, located in the east of the NW–SE extending Devonian Kelan volcanic‐sedimentary basin of the southern Altaides, occurs in the metamorphic rock series of the upper second lithological section of the lower Devonian lower Kangbutiebao Formation (D1k12). The Pb–Zn orebodies are stratiform and overprinted by late sulfide–quartz veins. Two distinct mineralization periods were identified: a submarine volcanic sedimentary exhalation period and a metamorphic hydrothermal mineralization period. The metamorphic overprinting period can be further divided into two stages: an early stage characterized by bedding‐parallel lentoid quartz veins developed in the chlorite schist and leptite of the ore‐bearing horizon, and a late stage represented by pyrite–chalcopyrite–quartz veins crosscutting chlorite schist and leptite or the massive Pb–Zn ores. Fluid inclusions in the early metamorphic quartz veins are mainly CO2–H2O–NaCl and carbonic (CO2±CH4±N2) inclusions with minor aqueous inclusions. The CO2–H2O–NaCl inclusions have homogenization temperatures of 294–368° C, Tm,CO2 of –62.6 to –60.5°C, Th,CO2 of 7.7 to 29.6°C (homogenized into liquid), and salinities of 5.5–7.4 wt% NaCl eqv. The carbonic inclusions have Tm,CO2 of –60.1 to –58.5°C, and Th, CO2 of –4.2 to 20.6°C. Fluid inclusions in late sulfide quartz veins are also dominated by CO2–H2O–NaCl and CO2±CH4 inclusions. The CO2–H2O–NaCl inclusions have Th,tot of 142 to 360°C, Tm,CO2 of –66.0 to –56.6°C, Th,CO2 of –6.0 to 29.4°C (homogenized into liquid) and salinities of 2.4–16.5 wt% NaCl eqv. The carbonic inclusions have Tm, CO2 of –61.5 to –57.3°C, and Th, CO2 of –27.0 to 28.7°C. The aqueous inclusions (L‐V) have Tm,ice of –9.8 to –1.3°C and Th,tot of 205 to 412°C. The P–T trapping conditions of CO2‐rich fluid inclusions (100–370 MPa, 250–368°C) are comparable with the late‐ to post‐regional metamorphism conditions. The CO2‐rich fluids, possibly derived from regional metamorphism, were involved in the reworking and metal enrichment of the primary ores. Based on these results, the Talate Pb–Zn deposit is classified as a VMS deposit modified by metamorphic fluids. The massive Pb–Zn ores with banded and breccia structures were developed in the early period of submarine volcanic sedimentary exhalation associated with an extensional subduction‐related back‐arc basin, and the quartz veins bearing polymetallic sulfides were formed in the late period of metamorphic hydrothermal superimposition related to the Permian–Triassic continental collision.

Geological and geochemical implications of the genesis of the Qolqoleh orogenic gold mineralisation, Kurdistan Province (Iran)

Abstract The Qolqoleh gold deposit is located in the northwestern part of the Sanandaj-Sirjan Zone (SSZ), within the NE-SW trending Qolqoleh shear zone. Oligocene granitoids, Cretaceous meta-limestones, schists and metavolcanics are the main lithological units. Chondrite-normalised REE patterns of the ore-hosting metavolcanics indicate REE enrichment relative to hanging wall (chlorite-sericite schist) and footwall (meta-limestone) rocks. The pattern also reflects an enrichment in LREE relative to HREE. It seems that the LREE enrichment is related to the circulation of SO4 2- and CO2-bearing fluids and regional metamorphism in the Qolqoleh shear zone. Both positive and negative Eu anomalies are observed in shear-zone metavolcanics. These anomalies are related to the degree of plagioclase alteration during gold mineralisation and hydrothermal alteration. In progressing from a metavolcanic protomylonite to an ultramylonite, significant changes occurred in the major/trace element and REE concentration. Utilising an Al-Fe-Ti isocon for the ore-hosting metavolcanics shows that Sc, Y, K, U, P, and M-HREE (except Eu) are relatively unchanged; S, As, Ag, Au, Ca, LOI, Rb and LREE are enriched, and Sr, Ba, Eu, Cr, Co and Ni decrease with an increasing degree of deformation. Based on geochemical features and comparison with other well-known shear zones in the world, the study area is best classified as an Isovolume-Gain (IVG) type shear zone and orogenic type gold mineralisation. Based on the number of phases observed at room temperature and their microthermometric behaviour, three fluid inclusion types have been recognised in quartz-sulphide and quartz-calcite veins: Type I monophase aqueous inclusions, Type II two-phase liquid-vapour (L-V) inclusions which are subdivided into two groups based on the homogenisation temperature (Th): a) L-V inclusions with Th from 205 to 255°C and melting temperature of last ice (Tm) from -3 to -9°C. b) L-V inclusions with higher Th from 335 to 385°C and Tm from -11 to -16°C. Type III three-phase carbonic-liquid inclusions (liquid water-liquid CO2-vapour CO2) with Th of 345-385°C. The mean values of the density of ore-forming fluids, pressure and depth of mineralisation have been calculated to be 0.79-0.96 gr/cm3, 2 kbar and 7 km, respectively. The δ18Owater and δD values of the gold-bearing quartz-sulphide veins vary from 7.2‰ to 8‰ and -40.24‰ to -35.28‰, respectively, which are indicative of an isotopically heavy crustal fluid and likely little involvement of meteoric fluid. The δ18Owater values of the quartz-calcite veins have a range of -5.31‰ to -3.35‰, and the δD values of -95.65‰ to -75.31‰, which are clearly lower than those of early-stage quartz-sulphide-gold veins, and are close to the meteoric water line. Based on comparisons of the D-O isotopic systematics, the Qolqoleh ore-mineralising fluids originated from metamorphic devolatilisation of Cretaceous volcano-sedimentary piles. Devolatilisation of these units occurred either synchronously with, or postdates, the development of penetrative (ductile) structures such as shear zones and during overprinting brittle deformation

Regional dome evolution and its control on ore-grade distribution: Insights from 3D implicit modelling of the Navachab gold deposit, Namibia

We introduce a novel approach to analyse and assess the structural framework of ore deposits that fully integrates 3D implicit modelling in data-rich environments with field observations. We apply this approach to the early Palaeozoic Navachab gold deposit which is located in the Damara orogenic belt, Namibia. Compared to traditional modelling methods, 3D implicit modelling reduces user-based modelling bias by generating open or closed surfaces from geochemical, lithological or structural data without manual digitisation and linkage of sections or level plans. Instead, a mathematically defined spatial interpolation is used to generate 3D models that show trends and patterns that are embedded in large drillhole datasets. In our 3D implicit model of the Navachab gold deposit, distinctive high-grade mineralisation trends were identified and directly related to structures observed in the field. The 3D implicit model and field data suggest that auriferous semi-massive sulphide ore shoots formed near the inflection line of the steep limb of a regional scale dome, where shear strain reached peak values during fold amplification. This setting generated efficient conduits and traps for hydrothermal fluids and associated mineralisation that led to the formation of the main ore shoots in the deposit. Both bedding-parallel and highly discordant sets of auriferous quartz-sulphide veins are interpreted to have formed during the later lock-up stage of the regional scale dome. Additionally, pegmatite dykes crosscut and remobilise gold mineralisation at the deposit scale and appear to be related to a younger joint set. We propose that kilometre-scale active folding is an important deformation mechanism that influences the spatial distribution and orientation of mineralisation in ore deposits by forming structures (traps and pathways for fluids) at different preferred sites and orientations. We also propose that areas that experience high shear strain, located along the inflection lines of folds can act as preferred sites for syn-deformational hydrothermal mineralisation and should be targeted for regional scale exploration in fold and thrust belts. Our research also suggests that examination of existing drillhole datasets using 3D implicit modelling is a powerful tool for spatial analysis of mineralisation patterns. When combined with fieldwork, this approach has the potential to improve structural understanding of a variety of ore deposits.

Polygenetic Compound Mineralization of Guoluolongwa Gold Field, Qinghai

two stages. Based on microthermometic study, three types of fluid inclusions are divided, namely aqueous inclusions (type I), aqueous-CO2 inclusions (type II) and pure CO2 inclusions (type III). The majority of type I and type II inclusions of stage B and type I inclusions of stage C often appear in groups, representing their primary causes. Besides, near the sulfide veinlet of stage C, many type I inclusions of stage B are arranged in rows along the fracture, showing characteristics of secondary inclusions, these inclusions may be formed at the same time with primary type I inclusions of stage C. So, there may be two main stages of inclusion formation, related to B and C stages, respectively. Stage B develops type I, type II, and type III inclusions, while stage C mainly contains type I inclusions. Homogenization temperatures and salinities of fluids are different in different stages. Mineralization of Guoluolongwa is mainly gold bearing quartz veins and quartz sulfide veins superimposed on the milky quartz veins. The early milky quartz veins of stage A may represent the product of low-grade metamorphic hydrothermal activity. Inclusions of stage B, including all these three types, are primary causes. Coexistence of aqueous and carbonaceous inclusions illustrates the separation of H2 O and CO 2. With a medium homogenization temperature ranging from 240℃ to 300℃, and salinities varing between 18~24% and 3~10% for type I and type II inclusions, respectively, fluid of stage B may be derived from metamorphic hydrothermal fluid. Stage C is characterized by type I inclusions with high salinity, ranging from 15% to 22%, shows that fluid may originate from magmatic hydrothermal, belongs to magmatic hydrothermal period. Homogenization

Fluid inclusion characteristics and geological significance of the Dajinshan W–Sn polymetallic deposit in Yunfu, Guangdong Province

The Dajinshan tungsten–tin polymetallic deposit is a quartz-vein-type ore deposit located in Western Guangdong Province. The ore bodies show a fairly simple shape and mainly occur as tungsten–tin polymetallic-bearing sulfide quartz veins, including quartz vein, quartz-greisens, and sulfide quartz veins, and their distribution is spatially related to Dajinshan granitoids. The formation of the deposit experienced three stages: a wolframite–molybdenite–quartz stage, a wolframite–cassiterite–sulfide–quartz stage, and a fluorite–calcite–carbonate stage. Based on detailed petrographic observations, we conducted microthermometric and Raman microspectroscopic studies of fluid inclusions formed at different ore-forming stages in the Dajinshan tungsten–tin polymetallic deposit, identifying four dominant types of fluid inclusions: aqueous two-phase inclusions, CO2-bearing inclusions, solid or daughter mineral-bearing inclusions, and gas-rich inclusions. The gas compositions of ore-forming fluids in the Dajinshan tungsten–tin polymetallic deposit are mostly CO2, CH4, and H2O. The hydrogen, oxygen, and sulfur isotopic data imply that the ore-forming fluids in the Dajinshan tungsten–tin polymetallic deposit were mainly derived from magmatic fluids, mixed with meteoric water in the ore-formation process. These results indicate that the fluid mixing and boiling led to the decomposition of the metal complex in ore-forming fluids and ore deposition.

The trinity pattern of Au deposits with porphyry, quartz–sulfide vein and structurally-controlled alteration rocks in Ciemas, West Java, Indonesia

The Ciemas gold mining area is located in the Sunda arc volcanic rock belt, West Java, Indonesia. Ore bodies are associated with Miocene andesite, dacite and quartz diorite porphyrite. To constrain ore genesis and mineralization significance, a detailed study was recently conducted examining these deposits, which included detailed field observation, petrographic study, petrochemistry, sulfur isotope analyses, zircon U–Pb dating, and fluid inclusion analysis. The results include the following findings. 1) Ore types have been identified as porphyry, a quartz–sulfide vein, and structure-controlled alteration rocks. 2) In host rocks, zircon LA–ICP-MS U–Pb dating of quartz diorite porphyrite, amphibole tuff breccia and andesite yield ages of 17.1±0.4Ma, 17.1±0.4Ma and 17.5±0.3Ma, respectively. 3) Fluid inclusions in the quartz from ore are given priority to liquid and gas–liquid phases, and their components are of the NaCl–H2O system with homogenization temperatures of 240–320°C, salinities of 14–17%, densities of 0.85–0.95g/cm3, and fluid pressure values between 4.1 and 46.8MPa, corresponding to metallogenic depths from 150 to 1730m. Fluid characteristics are identified as similar to those of high sulfur epithermal deposits. 4) The sulfur isotopic compositions are notably uniform, the δ34S values of wall rocks range from 3.71 to 3.85‰, and the δ34S values of ores vary from 4.90‰ to 6.55‰. The sulfur isotopic composition of ores is similar to that of the wall rocks, indicating a mixed origin of mantle with a sedimentary basement. 5) The trace element patterns of different ore types are similar, which indicates that they originate from the same source. Au deposits primarily occurred during the late magmatic activity. Finally, we have set up the regional metallogenic model, confirming that this gold deposit in the Sunda arc volcanic rock belt belongs to a metallogenic system from porphyry to epithermal type.

Types, characteristics and metallogenesis of gold deposits in the Jiaodong Peninsula, Eastern North China Craton

The Jiaojia type gold deposits in the Jiaodong Peninsula of the North China Craton represent an emerging major gold reserve, and constitute one of the two important types of gold deposits in China, the other being the Linglong type. The gold mineralization in these deposits can be subdivided into seven categories namely, altered-rock type in the fracture zone, gold-bearing quartz vein type, braided quartz vein type along fracture zones, quartz-sulfide vein type, interlayer type along the detachment belt, altered-conglomerate type and breccia type along the basin margin faults. The peak gold mineralization occurred during Early Cretaceous with the metallogeny controlled by extensive crust–mantle interaction. The deposits are hosted in the Early Precambrian basement and Mesozoic intrusions which experienced phyllic, sulfidic, silicic, and potassic alterations. The structures of the ore bodies include pinchout, repetition splay branches, composite, lateral tilting, echelon and imbrications. The upwelling of hot magma, fluid activity and extensional detachment resulted in the formation of extensive gold deposits in the Jiaodong Peninsula. The extensional detachment derived from magma upwelling provided favorable ore-hosting structure for the gold deposition. The ladder-type ore-hosting structures show variation from sharp to gentle dips with marked enrichment of the gold ores at the gentle angle of the fault segments and at the transition from steep to gentle dip angles, displaying a step-fault-controlled ore deposition. The formation of the gold deposits in the Jiaodong Peninsula coincided with the large-scale Early Cretaceous thinning of the lithosphere in the North China Craton, mainly controlled by extensional tectonics.

The Khopik porphyry copper prospect, Lut Block, Eastern Iran: Geology, alteration and mineralization, fluid inclusion, and oxygen isotope studies

The Khopik porphyry copper (Au, Mo) prospect in Eastern Iran is associated with a succession of Middle to Late Eocene I-type, high-K, calc-alkaline to shoshonite, monzonitic to dioritic subvolcanic porphyry stocks emplaced within cogenetic volcanic rocks. Laser-ablation U-Pb zircon ages indicate that the monzonite stocks crystallized over a short time span during the Middle Eocene (39.0±0.8Ma to 38.2±0.8Ma) as result of subduction of the Afghan block beneath the Lut block.Porphyry copper mineralization is hosted by the monzonitic intrusions and is associated with a hydrothermal alteration that includes potassic, sericitic-potassic, quartz-sericite-carbonate-pyrite (QSCP), quartz-carbonate-pyrite (QCP), and propylitic zones. Mineralization occurs as disseminated to stockwork styles, and as minor hydrothermal breccias. Some mineralization occurs in fault zones as quartz-sulfide veins telescoped onto the porphyry system. The main ore minerals are chalcopyrite and bornite with minorpyrite and magnetite and the highest Cu (0.01–0.9 wt. %), Au (>2ppm), and Mo (<80ppm) grades are closely associated with potassic alteration zones.Unidirectional, pre-ore stage solidification texture (UST) represented by comb-quartz layers within the potassic alteration zone formed from a hypersaline brine (57–73 wt. % NaCl equiv.), low density vapor-rich fluids (4–22 wt. % NaCl equiv.) at temperatures of 482 °C to over 600°C. The isotopic composition of oxygen (δ18Owater=8.7–8.9 ‰) suggests that the quartz layers crystallized from magmatic-hydrothermal fluids that exsolved in the upper part of the monzonitic intrusions. Potassic alteration formed from high salinity fluids (51–73 wt. %) at temperatures between 432–592°C, and low salinity vapor-rich solutions with 11–19 wt. % NaCl equiv. Later veinlets in the QSCP zone formed from lower salinity fluids (<47 wt. % NaCl equiv.) at temperatures between 332°–400°C. The oxygen isotopic data for the early alteration zones (δ18Owater=9–9.3 ‰ for potassic and 7.3 ‰ for QSCP) also indicate a magmatic origin for the ore fluids.The widespread presence of Middle Eocene to Lower Oligocene magmatism and mineralization in Eastern Iran suggests the presence of another important porphyry copper belt in addition to the northwest-southeast Urumieh-Dokhtar copper belt of Iran.

Quartz Vein Emplacement Mechanisms at the E26 Porphyry Cu-Au Deposit, New South Wales

Porphyry Cu-Au-Mo deposits are characterized by numerous fracturing events. Brittle fracture of mineralized intrusions and the surrounding host rocks is a consequence of hydraulic breakage caused by the interplay of the changing physiochemical properties of magmatic fluids and/or the local tectonic regime. We have mapped more than 1,400 quartz-sulfide vein sets at the Ordovician Endeavour 26 North (E26) deposit, central New South Wales, in order to constrain the processes influencing fracture development around small (∼200 m) porphyritic intrusions. Veins from intermediate levels in the E26 deposit define complicated patterns within 10 m of the porphyritic intrusions, whereas more systematic patterns occur up to 50 m from the intrusive contact. The outer parts of the ore deposit are characterized by quartz veins with orientations of ∼340° and subordinate orthogonal sets of bisecting veins at ∼240° and ∼290°. The data show a broad range of vein orientations that define a conical distribution around a vertical axis. There is a rare subset of near-horizontal veins that formed early relative to the main stage of ore-bearing vein emplacement. Many quartz veins exhibit fault displacements (at both micro- and macroscopic scales) and fabrics (including serrate fractures, slickenlines, and asymmetric fiber trails). The distribution of veins suggests that the dominant fracture array developed perpendicular to the direction of bulk finite extension, but significant vein dilation also occurred in orientations with a component of shear strain. We propose a physical model that combines intrusion-driven hydraulic fracturing into a preexisting fracture mesh to help explain the observed vein patterns and to better link fracture development and vein emplacement. Hydraulically driven deformation was important locally at E26, contributing to the formation of the irregular fracture stockwork immediately adjacent to the small intrusive bodies. The more predictable vein patterns that occur away from the porphyritic intrusions require part of the hydraulically driven extension to have reactivated the existing fracture mesh. Parts of this more systematic geometry, including the occurrence of flat veins, are probably related to the emplacement of larger (10-km diameter) magma bodies adjacent to E26, with doming causing the subordinate fracture arrays, including the gross conical distribution. Fluctuating fluid pressures, combined with hydraulically driven extension, caused dilation of preexisting and synmineralization fractures and superposition of veins with similar orientations. Vein patterns suggest that the regional stress state that existed prior to or synchronously with porphyry ore deposit formation strongly influenced vein orientation to within tens of meters away from the mineralizing intrusions. Fractures that localized ore in the E26 porphyry deposit developed in response to the infiltration of fluid batches, including magma and magmatic-hydrothermal fluids, into a regional deformation environment.

Fluid inclusions from the Jinchang Cu–Au deposit, Heilongjiang Province, NE China: Genetic style and magmatic-hydrothermal evolution

The Jinchang Cu–Au deposit is located in the easternmost part of the Central Asian Orogenic Belt (CAOB). The mineralization here is associated with Cretaceous porphyritic intrusions of ca. 120–110Ma and is mainly hosted within intensely altered Mesozoic granites, breccia pipes, ringed and radial faults. The gold ores are disseminated in the wall rock, and also occur as massive auriferous quartz-sulfide veins in fractures and breccias. Fluid inclusion data from breccias, chalcopyrite–quartz vein, and pyrite–quartz vein display homogenization temperatures in the range of 200 to >550°C and the fluids show variable salinity in the range of 0–58wt.% (NaCl equiv.). The halite absent fluid inclusions shows a slight increase in salinity with a sharp decrease in temperature. We interpret that the high-salinity brine and low salinity vapor- or aqueous-rich fluids from ores represent fluid unmixing from magma. The fluid inclusion data from Jinchang demonstrate that the main mineralization took place at temperatures from 480°C to 200°C, and evolved from high to low salinities. Geology and fluid inclusion data suggest that the Jinchang deposit is an oxidized intrusion-related Cu–Au deposit. The voluminous hydrothermal magnetite formed during high temperature potassic alteration of wall rocks in this ore deposit can be used as a potential prospecting tool.

Geology, geochemistry and ore genesis of the Wenyu gold deposit, Xiaoqinling gold field, Qinling Orogen, southern margin of North China Craton

The Wenyu giant gold deposit is hosted in the Precambrian Taihua Supergroup metamorphic rocks within the Xiaoqinling terrane (Qinling Orogen), on the southern margin of the North China Craton. The mineralization can be divided into three stages: quartz–pyrite veins early, quartz–sulfide veins middle (main), and carbonate–quartz veinlets late, with gold being mainly introduced in main stage. Quartz formed in two earlier stages contains three compositional types of fluid inclusions, i.e. pure CO2, CO2–H2O and NaCl–H2O, but the late-stage minerals only contain the NaCl–H2O inclusions. The inclusions in quartz formed in the early, main and late stages yield total homogenization temperatures of 262–417°C, 236–407°C and 114–239°C, respectively, with salinities no higher than 13wt.% NaCl equiv. Trapping pressures estimated from CO2–H2O inclusions are 139–399MPa and 111–316MPa in the early and main stages, corresponding to mineralization depths of 14km and 11km, respectively. Fluid boiling and mixing caused rapid precipitation of sulfides and native Au. Through boiling and inflow of meteoric water, the ore-forming fluid system evolved from CO2-rich to CO2-poor in composition, and from metamorphic to meteoric, as indicated by decreasing δ18Owater values from early to late. The carbon, sulfur and lead isotope compositions suggest the hostrocks within the Taihua Supergroup to be a significant source of ore metals. Integrating the data obtained from the studies including regional geology, ore geology, fluid inclusion and C–H–O–S–Pb isotope geochemistry, we conclude that the Wenyu gold deposit was an orogenic-type system formed in the tectonic transition from compression to extension during the Jurassic–Early Cretaceous continental collision between the North China and Yangtze Cratons.

Geological Characteristics and Exploration Potential of the NO.III Deposit in the Xiongcun District, Tibet, China

The Xiongcun district is located along the south margin of the Gangdese porphyry copper belt, approximately 53 km west of the Xigaze. No.III deposit is a newly discovered porphyry copper-gold deposit in the Xiongcun district. This paper first reports geological characteristics and exploration potential of No.III deposit. No.III deposit is hosted by Early Jurassic hornblende quartz diorite porphyry. Pervasive alteration is dominated by a well-mineralized potassic alteration. Major ore-bearing vein types include quartz-sulfide and chlorite-sulfide veins. Drilling holes and geochemical anomaly indicated the No.III deposit has excellent potential for exploration.