Precipitation Of Ore Minerals Research Articles

Tectono-magmatic factors for porphyry Cu-(Mo-Au) deposits formation: A case study from Pishtene ore deposit, Western Srednogorie, Bulgaria

Porphyry ore deposits are the source of much of the copper, molybdenum, gold and silver. Porphyry hydrothermal systems typically form in magmatic arcs above subduction zones. In this article, some key factors that may be involved in the formation of the Pishtene porphyry deposit in Western Srednogorie are outlined. The first process is the generation of magma in sub-arc mantle and enrichment of metals, water and other fluids. Next stage is а cyclic crystal fractionation in deep crustal magma chamber. There are a lot of other factors, such as a sulphide saturation, metal partitioning, precipitation of ore minerals, magmatic-hydrothermal evolution, erosional and weathering processes, but they are not discussed in this study.

Fluid provenance and genetic type of the Bubin Cu-Pb polymetallic deposit, Kohistan-Ladakh island arc, north Pakistan: Evidence from mineralogy, fluid inclusion and O-H-S-Pb isotopes

The Bubin Cu-Pb polymetallic deposit in Gilgit-Baltistan, Pakistan, is a well-known vein-type ore deposit located in the Kohitan-Ladakh island arc. Due to its significant economic importance as the most important deposit type in the Kohistan-Ladakh island arc, a comprehensive study on its ore genesis, fluids evolution, and genetic classification not only shed new light on our understanding the formation of such polymetallic deposit at a typical intra-oceanic arc, but also of help for the mineral exploration. Here, we present the results from electron probe micro-analyzer, fluid inclusions, Raman spectroscopy, and isotopic studies (O-H-S-Pb) to gain insights into the source of ore-forming fluids and materials, as well as the genetic-type and mechanism of ore precipitation for the Bubin deposit. The mineralization processes were divided into three main stages: Stage I (quartz-pyrite), Stage II (quartz-sulfide), and Stage III (quartz-carbonate). Stage II further comprised two sub-stages: IIa (quartz-chalcopyrite-magnetite) and IIb (quartz-galena-fahlore). The ore-forming fluids exhibited high to moderate temperatures (154–540 °C) and varying salinities (0.35–44.30 wt% NaCl) throughout the stages. Stage I fluids displayed critical behavior with high temperature and low salinity, and their isotopic signatures suggested a magmatic origin. Subsequently, the ore-forming fluids gradually evolved from primary magmatic origin to the mixing of meteoric water, as demonstrated by oxygen and hydrogen isotopic values (δ18Ofluid = -1.34 to 6.29 ‰, δD = -112.4 to −76.1 ‰). The δ34S values (-2.92 to 6.52 ‰) and Pb isotopic ratios (208Pb/204Pb = 39.06 to 40.93, 207Pb/204Pb = 15.72 to 15.99, and 206Pb/204Pb = 19.44 to 20.80) suggested a deep magmatic source for the ore-forming fluid, with metals primarily derived from the upper crust, likely associated with the Ladakh Batholith. Fluid boiling and maxing are the dominant mechanisms for ore mineral precipitation. Additionally, the high to moderate temperature and salinity, presence of solid-bearing and vapor rich inclusions, a Co/Ni ratio > 1, the Ni-As-Co diagram, and O-H-S-Pb isotopic evidence collectively support the classification of the Bubin Cu-Pb polymetallic deposit as an intrusion-related porphyry-style magmatic hydrothermal deposit.

The formation of lithium-rich pegmatites through multi-stage melting

Abstract Lithium-cesium-tantalum–type pegmatites (the primary source of lithium) crystallize from highly evolved, volatile felsic melts that incorporated crustal material in their source. Pegmatites are classically thought to form either from extreme fractionation of a parental granite body or via low-degree partial melting of a metamorphic rock (anatectic origin). However, the processes that lead to the formation of economic lithium pegmatite deposits remain enigmatic, because precipitation of lithium ore minerals requires melt lithium concentrations in excess of 5000 ppm—~500 times upper crustal abundances. We use petrological modeling to quantify lithium enrichment in an anatectic-origin scenario and show that it is primarily driven by the relative stability of residual biotite and muscovite at medium to high pressures (~8 kbar), and biotite and cordierite at low pressures (~3 kbar). We show anatexis of an average lithium-enriched metasedimentary source cannot sufficiently elevate the lithium content of the ensuing melt to form economic deposits; however, if this first-generation melt—now crystallized as granitic crust—is re-melted, the second-generation melt will be sufficiently concentrated in lithium to crystallize lithium ore minerals. We propose a petrogenetic model for anatectic-origin lithium pegmatites, in which a region experiences at least two stages of partial melting, ultimately generating lithium-rich melts without invoking extensive fractional crystallization. This mechanism can both account for the occurrence of unzoned lithium pegmatites and explain why economic pegmatites in many terranes are younger than their inferred source granites.

The role of zircon in hydrothermal heavy REE mineralisation: The case for unconformity-related ore deposits of north-west Australia

Zircon is hailed for its chemical and physical durability, but can undergo extensive chemical and structural modification due to radiation damage via the emission of alpha (α) particles, and subsequent low-temperature hydrothermal alteration. Here, we investigate Archean zircons from arkosic metasediments of the Browns Range Metamorphics (BRM) to evaluate their role in the formation of local unconformity-related heavy rare earth element (REE) ore deposits, within the Browns Range Dome, Western Australia. We determine that the heavy REE inventory of the BRM are primarily hosted in zircon, and that these zircons have a wide range of major element totals (77 to ~100 wt%, including low SiO2 and ZrO2 contents), and high and variable ‘non-formula’ components (U, Th, Y, REE, Nb, P, Al, Ca, Fe, Ti, F and OH− or H2O). Concentrations of Y + REE in some cases exceed 8 wt%. Extensive radiation damage (metamictisation) is confirmed by structural features including porous and amorphous domains, cavities, and voids. The lack of regional thermal events over an extended period likely prevented thermal annealing of these radiation-damaged zircons. Uptake of non-formula elements in metamict zircon, most likely during sedimentation in the late Archean, promoted further radiation damage, such that these grains remained highly susceptible to alteration by subsequent hydrothermal fluid circulation. We propose that the unconformity-related REE mineralisation was formed by saline fluids leaching Y + REE (and possibly P) from metamict zircon in the BRM, followed by ore mineral precipitation in fault zones near, and along the regional unconformity. More broadly, this model of ore formation may be relevant to other basin-hosted mineral systems, and could be used to guide exploration for unconformity-related REE deposits in Australia, and globally.

Geochronology, geochemistry, and genesis of the Shamai tungsten deposit, Inner Mongolia, NE China

AbstractThe Shamai tungsten deposit is located in the western part of the Xing'an Mongolian orogenic belt of northeastern China and contains quartz‐vein hosted tungsten mineralization. In this paper, we present the results of zircon laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) U–Pb dating of the fine‐grained biotite monzogranite, medium‐grained biotite monzogranite, and porphyritic biotite monzogranite samples from the deposit as well as in situ zircon Hf isotopic and in situ plagioclase Pb isotopic analyses. Combining new laser Raman spectroscopic data for fluid inclusions with previously HO isotopic data yields insights into the precipitation of ore minerals. The fine‐grained biotite monzogranite, medium‐grained biotite monzogranite, and porphyritic biotite monzogranite were emplaced at 142.5 ± 1.0 Ma, 141.9 ± 1.1 Ma, and 140.2 ± 1.0 Ma, respectively. The fine‐ to medium‐grained biotite monzogranite and porphyritic biotite monzogranite samples contain zircons with εHf(t) values from 3.2 to 7.9 and from 4.2 to 7.6, respectively, yielding tDM2 model ages from 996 to 692 Ma and 923 to 708 Ma, respectively. The geochemical, zircon Hf isotopic, and in situ plagioclase Pb isotopic data indicate that the magmas were generated by the partial melting of juvenile crustal material mixed with mantle‐derived components. The laser Raman and HO isotopic data for fluid inclusions within tungsten‐bearing quartz veins indicate that the tungsten mineralization formed as a result of fluid mixing. Combining the data with the spatial and temporal distribution and tectonic setting of tungsten deposits in NE China suggests that this area records four stages of mineralization at 300–290, 250–230, 200–180, and 150–130 Ma. The Shamai deposit occurred in an intra‐continental extensional regime.

Mineralogy of the scheelite-bearing ores of Monte Tamara, SW Sardinia: insights for the evolution of a Late Variscan W–Sn skarn system

AbstractSouthwestern Sardinia, Italy, hosts several skarn, W–Sn–Mo greisen and hydrothermal deposits related to a 289±1 Ma Late Variscan granite suite. Among them, the most representative scheelite-bearing skarns belong to the San Pietro and Sinibidraxiu localities, in the Monte Tamara area, Sulcis region. The San Pietro deposit is a typical calc-silicate skarn whereas Sinibidraxiu is a sharply bounded orebody hosted in a marble unit. Optical petrographic observations and compositional data of major and trace elements were obtained for samples from both localities. San Pietro data suggests evolution from an oxidising prograde skarn stage (andradite–diopside, hematite and scheelite), to progressively more reducing conditions from the early retrograde (magnetite–cassiterite) to the late sulfide stage (arsenopyrite, stannite, molybdenite, Bi sulfosalts and Zn–Cu–Pb–Fe sulfides); Sinibidraxiu has diffuse carbonate–quartz intergrowths pseudomorphic over an early mineral assemblage with fibrous habit, followed by abundant ore mineral precipitation under reducing conditions (scheelite, arsenopyrite and Pb–Zn–Cu–Fe sulfides). Geothermometers indicate a comprehensive temperature range of 460–270°C for the sulfide stages of both deposits. The differences between the two deposits might be controlled by the distance from the source intrusion coupled with the different reactivity of the host rocks. The San Pietro mineralogy represents a more proximal skarn, contrasting with more distal mineralogical and chemical features characterising the Sinibidraxiu orebody (lack of Mo–Sn–Bi phases; LREE–MREE–HREE signature of scheelite). This investigation contributes for the first time to the identification of a W–Sn skarn system in SW Sardinia, thereby suggesting the Monte Tamara area and its surroundings as favourable for further exploration.

From Fossil to Active Hydrothermal Outflow in the Back‐Arc of the Central Apennines (Zannone Island, Italy)

AbstractPost‐orogenic back‐arc magmatism is accompanied by hydrothermal ore deposits and mineralizations derived from mantle and crustal sources. We investigate Zannone Island (ZI), back‐arc Tyrrhenian basin, Italy, to define the source(s) of mineralizing hydrothermal fluids and their relationships with the regional petrological‐tectonic setting. On ZI, early Miocene thrusting was overprinted by late Miocene post‐orogenic extension and related hydrothermal alteration. Since active submarine hydrothermal outflow is reported close to the island, Zannone provides an ideal site to determine the P‐T‐X evolution of the long‐lived hydrothermal system. We combined field work with microstructural analyses on syn‐tectonic quartz veins and carbonate mineralizations, X‐ray diffraction analysis, microthermometry and element mapping of fluid inclusions (FIs), C, O, and clumped isotopes, and analyses of noble gases (He‐Ne‐Ar) and CO2 content in FIs. Our results document the evolution of a fluid system of magmatic origin with increasing mixing of meteoric fluids. Magmatic fluids were responsible for quartz veins precipitation at ∼125 to 150 MPa and ∼300°C–350°C. With the onset of extensional faulting, magmatic fluids progressively interacted with carbonate rocks and mixed with meteoric fluids, leading to (a) host rock alteration with associated carbonate and minor ore mineral precipitation, (b) progressive fluid neutralization, (c) cooling of the hydrothermal system (from ∼320°C to ∼86°C), and (d) embrittlement and fracturing of the host rocks. Both quartz and carbonate mineralizations show noble gases values lower than those from the adjacent active volcanic areas and submarine hydrothermal systems, indicating that the fossil‐to‐active hydrothermal history is associated with the emplacement of multiple magmatic intrusions.

The prograde-to-retrograde evolution of the Huangshaping skarn deposit (Nanling Range, South China)

Huangshaping is a world-class skarn deposit hosting abundant W–Sn polymetallic mineralization in the Nanling Range, South China. Although the geochemistry of skarn-hosted mineral deposits has been extensively studied, the role of the prograde-to-retrograde stage transition in the enrichment and precipitation of metallic elements in high-temperature systems has received little study to date. Here, we analyzed garnet, scheelite, and cassiterite in high-temperature granite porphyry-related W–Sn polymetallic system of the Huangshaping deposit to investigate these processes. Three generations of garnet (Grt I, Grt II, and Grt III), two generations of scheelite (Sch I and Sch II), and two types of cassiterite (Cst I and Cst II) were distinguished with regard to their mineral associations, microscopic characteristics, and geochemical features. The results show that grossular–andradite garnet formed from Al-rich andradite (Grt I, Al2O3: 8.18 wt%) in the early prograde stage and pure Fe-andradite (Grt III, Al2O3: 0.15 wt%) in the late prograde stage. Mo-rich scheelite (Sch Ia, MoO3: 19.41 wt%) formed in the prograde stage and coexisted with Grt III, sharing the same REE patterns. A shift from HREE enrichment in Grt I to HREE depletion in Grt III reflects progressive uptake of REEs by secondary mineral phases. Grt III has the highest average contents of W (905 ppm), Mo (19 ppm), and Sn (5610 ppm), suggesting an enrichment of metallic elements at the end of the prograde stage. In contrast, Mo-poor scheelite (Sch II, MoO3: 0.63 wt%) co-crystallized with molybdenite and fluorite in the retrograde stage and shares similar REE patterns with the granite porphyry. Skarn mineralization at Huangshaping was a two-step process controlled by metamorphic stage. The prograde stage was characterized by high temperatures and fO2 and a Cl-rich fluid, and it resulted in enrichment of ore-forming elements with minor scheelite precipitation. The retrograde stage was characterized by lower temperatures and fO2 and a F-rich fluid, and it resulted in major precipitation of ore minerals (scheelite, molybdenite, and cassiterite). Dissolution–reprecipitation reactions played an important role in extraction of metallic elements from decomposing anhydrous skarn minerals and formation of ore minerals. A decrease in the high-field-strength element (HFSE) content of cassiterite from proximal skarn (Cst I) to distal skarn (Cst II) indicates declining temperature accompanied by precipitation of fluorite. This study examines the transition from the prograde stage to the retrograde stage in the Huangshaping deposit, and it provides insights into the genesis of other skarn W–Sn polymetallic deposits in the Nanling magmatic–tectonic–metallogenic belt.

Geochemical, fluid inclusion and O–H–S isotope constraints on the origin of the Rangraz copper deposit, Central Iran

The Rangraz copper deposit (5 Mt @ 0.83% Cu) is located 20 km north of Saveh city, Markazi Province, Iran, in the central Uromieh-Dokhtar volcano-plutonic belt. Host rocks are mainly composed of Eocene volcanic and volcaniclastic rocks that have been intruded by late Eocene quartz monzodiorites and basaltic-andesitic dikes. The dominant copper-related hydrothermal alteration types include silicification, sericitization, and chloritization-kaolinitization. The ore body takes the form of fault-hosted, NW-SE-striking lodes comprising pyrite, chalcopyrite, bornite, specular hematite and magnetite as the principal hypogene ore minerals. Gold (maximum spot assays of up to ca. 0.37 ppm Au) and silver (up to 20.6 ppm Ag) have also been recorded. The ore minerals are mainly confined to veins or veinlets showing crustiform, colloform, open space-filling, dissemination and replacements characteristics in texture. The principal gangue minerals are quartz, barite and calcite. Most of the fluid inclusions identified in quartz-chalcopyrite ± specular hematite veins contain two liquid and vapour phases at room temperature. The primary and pseudo-secondary fluid inclusions have low to intermediate homogenization temperatures between 134 and 338 °C and salinities between 3.55 and 16.89 wt% NaCl equivalents. The fluid inclusion data are consistent with a two-stage evolution of the mineralizing system with initial metal precipitation at crustal depths of <2 km followed by a later pulse of metal deposition at shallower crustal levels of <1 km. The calculated 34SH2S values of sulphide mineral separates from the Rangraz copper deposit range from −9.1‰ to −7.3‰, whereas the calculated δD and δ18O values of the ore fluids range from −3.2 to 0.4‰ and −85 to −75‰, respectively. The δ34S values of the Rangraz samples are consistent with a magmatic sulphur source, implying a possible link between copper mineralization and the Rangraz quartz-monzodiorite. The H, S and O isotope data are consistent with extensive mixing of primary magmatic fluids with cooler, oxidizing meteoric waters occurred in the Rangraz deposit and was responsible for triggering the precipitation of ore minerals. Collectively, the fluid inclusion and isotope data point towards the copper-bearing fluids having been subjected to dilution and cooling, probably as a consequence of their mixing with meteoric waters and boiling. Taken as a whole, the geological setting, ore and gangue mineralogy, vein textures, hydrothermal alteration types, and geochemical, stable isotope, and fluid inclusion evidence may be taken to imply that the Rangraz copper deposit belongs to a class of vein-hosted low sulfidation epithermal mineral systems, several of which have been recorded in the Uromieh-Dokhtar magmatic arc.

Zinc-bearing ferromanganese mineralization in a rift-marginal carbonate platform, Red Sea, Egypt: Reconstruction of an epigenetic-supergenetic system

Polymetallic mineralization hosted by rift marginal carbonate preserves a comprehensive archive that enables reconstruction of the initiation and evolution of rifting. The present study focuses on a Miocene shallow marine succession and related polymetallic (Fe-Mn-Zn) ores at the Um Greifat area along the Red Sea coast in the Central Eastern Desert of Egypt. The study area represents a unique Early-Middle Miocene syntectonic marginal carbonate platform of shallow marine and coastal plain facies. The carbonate-clastic succession comprises two units, lower and upper, that are separated by a magnesite bed. Dolomitization, karstification, fracturing and brecciation are the main diagenetic features, which allow reconstructing fluctuations of sea level induced by tectonic uplift and rifting.The polymetallic nonsulfide mineralization comprises mainly Fe-Mn-Zn oxides, forming a stratiform and strata-bound ore bodies in the lower unit of the succession and/or lenticular and cavernous masses in the upper unit. The mineralogy is dominated by chalcophanite, hetaerolite, goethite, hematite and smithsonite besides zincite, pyrolusite, cryptomelane, franklinite, coronadite, quartz and alunite-natroalunite. Less common siderite, pyrite and chalcopyrite are observed. Crystal morphologies, texture and distribution of the ferromanganese minerals were modified depending on the textures, porosity, open-spaces and discontinuities of their host carbonate. The mode of occurrence, texture, mineralogy and geochemistry of the polymetallic ores suggest a two epigenetic-supergene origin. The early stage encompassed precipitation of sulfides, silica and/or circulation of highly acidic metal-rich hydrothermal solutions through faulted carbonate blocks. Dissolution and intensive oxidation of primary sulfides, Fe+2 and Mn+2 in oxic and supergenetic conditions resulted in the formation of polymetallic oxides that represent the late stage. Major uplifting and exhumation by the Red Sea extension, along with circulation of low-temperature hydrothermal fluids through faulted areas, initiated ore mineral precipitation under near-neutral to mildly acidic conditions. The interplay of diagenesis, deformation, tectonism and hydrothermalism was likely enhanced by rift-induced geothermal activity in the Red Sea basin and adjacent areas.

Superimposed mineralization at the Suoerkuduke Cu–Mo skarn Deposit, North Xinjiang, China

The Suoerkuduke Cu–Mo skarn deposit is located in Fuyun County, Xinjiang Uygur Autonomous Region in NW China, within the northern margin of the East Junggar block. Comprehensive studies of ore deposits demonstrate that the deposit features two episodes of skarn mineralization: the first (Episode A) skarn is stratiform or lenticular and is characterized by predominantly disseminated Fe–Cu–Mo ores, whereas the second (Episode B) skarn occurs as veins or stockworks and contains predominantly Cu–Mo–Zn ores.Episode A mineralization formed in the Late Devonian (379.2 ± 2.8 Ma), whereas Episode B mineralization formed in the Early Permian (296.6 ± 1.9 Ma). Episode A skarn was genetically linked to dacite/syenite porphyries and may have occurred in an island arc setting, whereas Episode B skarn was genetically linked to granite porphyry (295.3 ± 3.8 Ma) and may have developed in a postcollisional setting.Based on mineral paragenesis and crosscutting relationships, the hydrothermal mineralizing event of Episode A is further divided into three stages, i.e., the prograde (A1), oxide (A2), and retrograde (A3) stages, while that of Episode B is divided into four stages, i.e., the prograde (B1), retrograde (B2), quartz-sulfides (B3) and quartz-carbonate (B4) stages. Three types and seven subtypes of fluid inclusions (L-, V- and S1- to S5-types) are distinguished based on fluid compositions and phase assemblages.Episode A ore-forming fluid (H2O–NaCl) system involved two major mineralizing events: (1) the first fluid boiling (stage A1) at 530–560 °C and lithostatic pressures of 550–800 bar and (2) the second fluid boiling (stage A3) at 370–420 °C and hydrostatic pressures of 200–300 bar. Episode B ore-forming fluid (H2O–NaCl–KCl) system involved four major mineralizing events: (1) the first fluid boiling (stage B1) at 530–580 °C and lithostatic pressures of 600–850 bar, (2) the second fluid boiling (stage B3) at 320–360 °C and hydrostatic pressures of 100–200 bar, (3) overpressure trapping; brine inclusions homogenized by halite dissolution can be explained as a result of entrapment under overpressure condition, and (4) mixing with meteoric water (stage B4). Fluid boiling was the predominant ore-forming mechanism, while mixing between magmatic and meteoric fluids may also have contributed to ore mineral precipitation (mainly for sphalerite) in Episode B to a lesser extent.

Geochemistry of ore-forming fluids, Deh-Salm uneconomic porphyry Mo system, SW Nehbandan, Iran: a fluid inclusion investigation

ABSTRACTBased on the fluid inclusion and rock sample geochemistry in Deh-Salm hydrothermal system, it is shown that uneconomic molybdenite mineralization occurred in both stockwork- and limited skarn-type alterations. Homogenization temperatures and salinities based on microthermometry data are presented for fluid inclusions from hydrothermal quartz associated with pyrite, galena, sphalerite and rare molybdenite mineralization. The data indicate that ore mineral precipitation occurred within a temperature range of 250° to > 490°C from moderate to high-salinity (9 to > 42 wt% NaCl equivalent) aqueous fluid. Two stages of hydrothermal activity characterized by high-salinity fluids (> 30 wt% NaCl equivalent) are identified; 1) relatively high-temperatures (350° to > 490°C); 2) lower temperatures (170° to 250°C). The high-salinity, high-temperature stage is interpreted to be the evidence for resurgent boiling. Dilution of these fluids by convicting meteoric water resulted in low to moderate salinity fluids, which dominated the inclusion population in quartz hosted crystals. The high-salinity, low-temperature fluid inclusions identify the residual fluids derived from boiling which happened as a result of a change in the pressure regime from dominantly lithostatic to hydrostatic conditions. Condensation and infiltration of ground waters caused major chemical variations, increasing the hydrostatic pressure, and the acid-washed processes on the system. The intense acid-washed and the intrusive rock depth is suggested to be the main reasons caused an uneconomic metal deposition in Deh-Salm system.

Geology, Geochemistry and Hydrothermal Fluid Characteristics of Low Sulfidation Epithermal Deposit in the Sangon Area, Kokap, Special Region of Yogyakarta

On the basis of the previous studies and reconnaissance survey in the studyarea covering Sangon, Kalirejo, Kokap Sub-district, Kulon Progo Regency, Special Region of Yogyakarta, it reveals some facts of the occurrence of quartz veins with massive, crustiform, comb, drusy cavity, saccharoidal, granular, and reniform/mammillated textures, the appearance of lattice bladed barite and hydrothermal breccia veins. Referring to those characteristics, the deposit type in the study area is interpreted to be low sulfidation epithermal type. This study is aimed to understand and characterize the geological condition, rock and ore geochemistry and the mineralizing fluids. The alteration and ore mineralization are almost observed in entire rock units particularly the intrusive andesite 1. Their formation is controlled by the tension fractures (NW–SE and NE–SW) which associate with sinistral strike slip faults (NE–SW), dilational jog (NNW–SSE), oblique normal fault (WNW–ESE), and predictable normal fault at the NE of study area (NW–SE). The alteration zones are developed to be silica-clay (quartz-illite-kaolinite-kaolinite/smectite), argillic (smectite-illite/smectite), and propylitic (chlorite-calcite±epidote). The precipitationof ore minerals is controlled by boiling, mixing, and wall-rock alteration, and canbe found in the quartz veins (quartz-adularia-sericite) and disseminated in the alteration zones, which their high variability is only can be found in the quartz veins, including pyrite, sphalerite, chalcopyrite, galena, marcasite, and arsenopyrite. Based on the ICPAES measurement of 5 quartz vein samples, the Cu, Zn, Pb, and As grade reach about 5,171 ppm, 8,995 ppm, 6,398 ppm, 34.1 ppm, and 1,010.5 ppm, respectively. Gold is not detected. Fluid inclusion microthermometric analysis shows Th of 242.1–257.6 °C and salinity of 1.57–3.87 wt.% NaCl equiv., which indicate a depth below the paleosurface of 384–516 m, and pressure of 101.7–136.6 bar. The ore deposit in the study area is interpreted to be a deep basemetal low sulfidation epithermal type. Gold might be depleted in this epithermal type.

Fluid evolution in a volcanic-hosted epithermal carbonate–base metal–gold vein system: Alto de la Blenda, Farallón Negro, Argentina

Alto de la Blenda is a ∼6.6-Ma intermediate-sulphidation epithermal vein system in the Farallon Negro Volcanic Complex, which also hosts the 7.1-Ma porphyry–Cu–Au deposit of Bajo de la Alumbrera. The epithermal vein system is characterised by a large extent and continuity (2 km × 400 m open to depth × 6 m maximum width) and an average gold grade of ∼8 g/t. The vein is best developed within an intrusion of a fine-grained equigranular monzonite, interpreted as the central conduit of a stratovolcano whose extrusive activity ended prior to porphyry–Cu–Au emplacement at Bajo de la Alumbrera, which is in turn cut by minor epithermal veins. The Alto de la Blenda vein consists predominantly of variably Mn-rich carbonates and quartz, with a few percent of pyrite, sphalerite, galena and other sulphide and sulphosalt minerals. Four phases of vein opening, hydrothermal mineralisation and repeated brecciation can be correlated between different vein segments. Stages 2 and 3 contain the greatest fraction of sulphide and gold. They are separated by the emplacement of a polymictic breccia containing clasts of quartz feldspar porphyry as well as basement rocks. Fluid inclusions in quartz related to stages 2 to 4 are liquid rich with 2–4 wt% NaCl(eq). They homogenise between 160 and 300 °C, with very consistent values within each assemblage. Vapour inclusions are practically absent in the epithermal vein. Quartz fragments in the polymictic breccia contain inclusions of intermediate to vapour-like density and similar low salinity (∼3 wt% NaCl(eq)), besides rare brine inclusions containing halite. Laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) analyses of epithermal inclusions indicate high concentrations of K, Fe, As, Sb, Cs, and Pb that significantly vary within and through subsequent vein stages. Careful consideration of detection limits for individual inclusions shows high gold concentrations of ∼0.5 to 3 ppm dissolved in the ore fluid, which contains variably high sulphur concentrations in excess over Fe and other chalcophile metals. Compositional variations are interpreted to reflect cooling and contraction of lower-density magmatic fluids at depth, like those preserved in porphyry clasts that were mechanically transported up by the polymictic breccia. Ore mineral precipitation from the magmatic fluid occurred by further cooling and possibly minor mixing with surface-derived water, leading to sulphide saturation, de-sulphidation of the magmatic fluid and consequent gold precipitation. The absence of flash boiling and/or reduction by carbonaceous host rocks has led to relatively modest but constant gold grades in the carbonate–base metal–gold veins of Alto de la Blenda.

Mineralogy and geochemistry of indium-bearing polymetallic veins in the Sarvlaxviken area, Lovisa, Finland

A number of polymetallic vein mineralizations of different styles and metal associations, including base, alloy, noble and critical metals, have been discovered around the Sarvlaxviken bay in the westernmost parts of the Mesoproterozoic Wiborg Batholith, south-eastern Finland. The veins occur in two rapakivi granite varieties: coarse-grained wiborgite; and medium-grained Marviken granite. The veins are divided into five groups based on the dominant metal associations.The Li–As–W–Zn–Mn, Pb–Zn and Cu–As–In associations are hosted by wiborgite, and are strongly controlled by a NNW-trending tectonic pattern that evolved in two main stages. The Li–As–W–Zn–Mn association (generation 1) formed in a typical greisen environment with Li-bearing mica in significant alteration halos around a narrow quartz vein. This greisenization was accompanied by silicification, followed by sericitization and chloritization. The Pb–Zn association occurs in a similar vein type but without typical high-temperature minerals and is considered to have formed at a higher crustal level. Generations 2a and 2b formed under more brittle conditions leading to fracturing, quartz veining and metal precipitation of ore minerals. This metal association is characterized by very high contents of Cu, As and up to 1490ppm In but with ≤0.4% Zn, which leads to very high In/Zn ratios (up to 8400) enabling formation of abundant roquesite.The As–Sn–Cu and Mo–Bi–Be associations are hosted by alteration zones without hydrothermal quartz in the Marviken granite. Mineralization with moderately high contents of As, Sn and Cu is associated with greisenization while mineralization with spectacular contents of Be as well as high contents of Mo and Bi is associated with sericitization, chloritization and berylification.The internal age relations between the wiborgite-hosted, NNW-trending veins show a clear evolution from a typical greisen type environment (the Li–As–W–Zn–Mn and Pb–Zn associations of generation 1) to cooler and more brittle conditions governing quartz veining and precipitation of ore minerals belonging to the Cu–As–In association (generations 2a and 2b). The age relations between these wiborgite-hosted veins and the veins in the Marviken granite are more uncertain but the presence of a NS-trending granitic dyke on the eastern side of the Sarvlaxviken bay, with similar ore-fertile geochemical composition as the Marviken granite, indicates that the tectonically controlled veins formed simultaneously with the emplacement of the Marviken granite and associated hydrothermal activity.The polymetallic veins in the Sarvlaxviken bay are unique for the Fennoscandian Shield, not the least for the locally high indium grades and spectacular roquesite grains. There is an obvious exploration potential for similar veins (and hence a number of base, alloy, noble and critical metals) also elsewhere in the entire Wiborg Batholith.

The Patricia Zn–Pb–Ag epithermal ore deposit: An uncommon type of mineralization in northeastern Chile

The Patricia ore deposit represents an unusual example of economic Zn–Pb–Ag mineralization at the northernmost end of the Late Eocene–Oligocene metallogenic belt in Chile. It is hosted by volcano-sedimentary units, which are typically tuffaceous and andesitic breccias. The ore body consists of a set of subvertical E-W vein systems developed under a sinistral strike-slip regime that included transtensive domains with generalized extensional structures where the ores were deposited. The deposit is divided into two blocks by a set of NNW-ESE-trending reverse faults, which uplifted the eastern block and exhumed thicker and deeper parts of the deposit. At least 200m of volcano-sedimentary pile hosting the mineralization has been eroded in this block. By contrast, the western block exposes a shallower part of the system where cherts, amorphous silica and jasperoids occur. Three main stages of mineralization have been defined: (1) pre-ore stage is characterized by early quartz, pyrite and arsenopyrite, (2) base-metal and silver stage; characterized by sphalerite (6 to 15mol% FeS), galena, chalcopyrite, pyrrhotite and Ag-bearing minerals (freibergite, polybasite, stephanite, pyrargyrite, freieslebenite and acanthite) and (3) post-ore stage; characterized by late quartz, kutnohorite and minor sulfides (arsenopyrite, sphalerite, pyrite, galena, Ag-bearing minerals and Pb-sulfosalts). Whole-ore geochemistry shows two groups of elements that are positively correlated; 1) Ag–Cd–Cu–Pb–Zn related to the base metal sulfides and 2) Au–As–Ge–Sb–W related to arsenopyrite and pyrite. Hydrothermal alteration is pervasive in the outcropping mineralized areas, including silicification and locally, vuggy silica textures. At depth, chloritic and sericitic alteration is developed along vein selvages and is superimposed to the regional propylitic alteration. Fluid inclusions indicate that the base-metal ores were deposited from 250 to 150°C moderate salinity fluids (1–9wt.% NaCl). The pre-ore stage is characterized by a saline fluid (6–22wt.% NaCl) and between 210 and 250°C whereas the post-ore stage has salinity of 4–8wt.% and temperature from 175 to 215°C. Cooling was the mechanism of ore mineral precipitation in the Patricia deposit, although mixing of fluids could have occurred in the pre-ore stage. Mineralogical, geochemical and fluid inclusion evidence is consistent with an intermediate sulfidation (IS) epithermal deposit type. This study highlights the high potential for hidden economic mineralization at depth in the western block and for extension of the ore body both to the south and to deeper levels in the eastern block of the Patricia ore deposit. To a larger extent, the implications of finding such polymetallic epithermal style of mineralization in the northern Chile Precordillera is relevant both to the regional metallogenic perspective and to the exploration potential of the region, where the late Eocene–early Oligocene metallogenic belt apparently disappears.

Geology, Geochemistry, and Genesis of the Tongcun Reduced Porphyry Mo (Cu) Deposit, NW Zhejiang Province, China

The Tongcun Mo (Cu) deposit in Kaihua city of Zhejiang Province, eastern China, occurs in and adjacent to the Songjiazhuang granodiorite porphyry and is a medium‐sized and important porphyry type ore deposit. Two irregular Mo (Cu) orebodies consist of various types of hydrothermal veinlets. Intensive hydrothermal alteration contains skarnization, chloritization, carbonatization, silicification and sericitization. Based on mineral assemblages and crosscutting relationships, the ore‐forming processes are divided into five stages, i.e., the early stage of garnet + epidote ± chlorite associated with skarnization and K‐feldspar + quartz ± molybdenite veins associated with potassic‐silicic alteration, the quartz‐sulfides stage of quartz + molybdenite ± chalcopyrite ± pyrite veins, the carbonatization stage of calcite veinlets or stockworks, the sericite + chalcopyrite ± pyrite stage, and the late calcite + quartz stage. Only the quartz‐bearing samples in the early stage and in the quartz‐sulfides stage are suitable for fluid inclusions (FIs) study. Four types of FIs were observed, including 1) CO2‐CH4 single phase FIs, 2) CO2‐bearing two‐ or three‐phase FIs, 3) Aqueous two‐phase FIs, and 4) Aqueous single phase FIs. FIs of the early stages are predominantly CO2‐ and CH4‐rich FIs of the CO2‐CH4‐H2O‐NaCl system, whereas minerals in the quartz‐sulfides stage contain CO2‐rich FIs of the CO2‐H2O‐NaCl system and liquid‐rich FIs of the H2O‐NaCl system.For the CO2‐CH4 single phase FIs of the early mineralization stage, the homogenization temperatures of the CO2 phase range from 15.4 °C to 25.3 °C (to liquid), and the fluid density varies from 0.7 g/cm3 to 0.8 g/cm3; for two‐ or three‐phase FIs of the CO2‐CH4‐H2O‐NaCl system, the homogenization temperatures, salinities and densities range from 312°C to 412°C, 7.7 wt% NaCl eqv. to 10.9 wt% NaCl eqv., and 0.9 g/cm3 to 1.0 g/cm3, respectively. For CO2‐H2O‐NaCl two‐ or three‐phase FIs of the quartz‐sulfides stage, the homogenization temperatures and salinities range from 255°C to 418°C, 4.8 wt% NaCl eqv. to 12.4 wt% NaCl eqv., respectively; for H2O‐NaCl two‐phase FIs, the homogenization temperatures range from 230 °C to 368 °C, salinities from 11.7 wt% NaCl eqv. to 16.9 wt% NaCl eqv., and densities from 0.7 g/cm3 to 1.0 g/cm3. Microthermometric measurements and Laser Raman spectroscopy analyses indicate that CO2 and CH4 contents and reducibility (indicated by the presence of CH4) of the fluid inclusions trapped in quartz‐sulfides stage minerals are lower than those in the early stage.Twelve molybdenite separates yield a Re‐Os isochron age of 163 ± 2.4 Ma, which is consistent with the emplacement age of the Tongcun, Songjiazhuang, Dayutang and Huangbaikeng granodiorite porphyries. The δ18OSMOW values of fluids calculated from quartz of the quartz‐sulfides stage range from 5.6‰ to 8.6‰, and the δDSMOW values of fluid inclusions in quartz of this stage range from – 71.8‰ to 88.9‰, indicating a primary magmatic fluid source. δ34SV‐CDT values of sulfides range from +1.6‰ to +3.8‰, which indicate that the sulfur in the ores was sourced from magmatic origins.Phase separation is inferred to have occurred from the early stage to the quartz‐sulfides stage and resulted in ore mineral precipitation. The characteristics of alteration and mineralization, fluid inclusion, sulfur and hydrogen‐oxygen isotope data, and molybdenite Re‐Os ages all suggest that the Tongcun Mo (Cu) deposit is likely to be a reduced porphyry Mo (Cu) deposit associated with the granodiorite porphyry in the Tongcun area.

Ore geology, fluid inclusions and four-stage hydrothermal mineralization of the Shangfanggou giant Mo–Fe deposit in Eastern Qinling, central China

The Eastern Qinling, Central China, containing more than 20 Mesozoic porphyry±skarn systems, is the most important Mo province in the world. The Shangfanggou giant Mo deposit, Luanchuan County, Henan Province, is a porphyry-skarn system hosted in a lithologic association comprising carbonaceous sandstone, shale, carbonate and chert within the Neoproterozoic Luanchuan Group. Mo ores are mainly altered porphyry, skarn and hornfels, with minor altered gabbro. The mineralization process includes four stages, potassic alteration of the porphyry and skarnization of dolomite marble in stage 1, stockworks of quartz+molybdenite±sulfide (stage 2), pyrite+quartz±sulfides (stage 3), and carbonate±quartz±fluorite (stage 4), respectively. Mo mineralization was generally associated with strong silicification and/or phyllic alteration. The fluid inclusions in minerals include three compositional types, i.e., CO2-bearing (C-type), aqueous (W-type) and daughter mineral-bearing (S-type). Minerals formed in stages 1 to 3 contain all the three types of FIs, but the stage 4 minerals only contain the W-type FIs. Oxides and Cu-phosphate are recognized as daughter minerals in S-type inclusions in minerals of stage 1, whereas the daughter sulfide and reducing gases such as CO, CH4, H2S and C2H6 can be observed in quartz of stages 2 and 3, suggesting that the ore-forming fluids were initially oxidizing and then evolved to reducing. Boiling fluid inclusion assemblages can be observed in minerals formed in stage 2 or earlier, but not in stage 3 or later. Fluid boiling caused CO2 escape, oxygen fugacity decrease and rapid precipitation of ore minerals, and was a key factor causing Mo-mineralization at Shangfanggou. Data and interpretations presented in this contribution show that the fluids forming the Shangfanggou Mo deposit evolved from CO2-rich, high-salinity hypothermal, to CO2-poor, low-salinity epithermal (low-T). The Mo mineralization at the Shangfanggou deposit mainly occurred at depth of 6.6–7.0km, deeper than the majority of porphyry systems in volcanic arcs, which resulted from a CO2-rich magma–fluid system originating from partial melting of thickened lower crust. The Shangfanggou mineral system developed during 158–134Ma when the Yangtze–North China continental collision began to evolve from compression to extension. Magmatic hydrothermal deposits developed in a continental collision regime are generally formed by CO2-rich, high-salinity fluids.

The Physical Hydrogeology of Ore Deposits

Hydrothermal ore deposits represent a convergence of fluid flow, thermal energy, and solute flux that is hydrogeologically unusual. From the hydrogeologic perspective, hydrothermal ore deposition represents a complex coupled-flow problem—sufficiently complex that physically rigorous description of the coupled thermal (T), hydraulic (H), mechanical (M), and chemical (C) processes (THMC modeling) continues to challenge our computational ability. Though research into these coupled behaviors has found only a limited subset to be quantitatively tractable, it has yielded valuable insights into the workings of hydrothermal systems in a wide range of geologic environments including sedimentary, metamorphic, and magmatic. Examples of these insights include the quantification of likely driving mechanisms, rates and paths of fluid flow, ore-mineral precipitation mechanisms, longevity of hydrothermal systems, mechanisms by which hydrothermal fluids acquire their temperature and composition, and the controlling influence of permeability and other rock properties on hydrothermal fluid behavior. In this communication we review some of the fundamental theory needed to characterize the physical hydrogeology of hydrothermal systems and discuss how this theory has been applied in studies of Mississippi Valley-type, tabular uranium, porphyry, epithermal, and mid-ocean ridge ore-forming systems. A key limitation in the computational state-of-the-art is the inability to describe fluid flow and transport fully in the many ore systems that show evidence of repeated shear or tensional failure with associated dynamic variations in permeability. However, we discuss global-scale compilations that suggest some numerical constraints on both mean and dynamically enhanced crustal permeability. Principles of physical hydrogeology can be powerful tools for investigating hydrothermal ore formation and are becoming increasingly accessible with ongoing advances in modeling software. * ### Notation a : total fracture aperture after dilation a : initial aperture A : cross sectional area [L2] b : thickness [L] c : specific heat capacity (usually isobaric heat capacity) [E M−1 T−1] c b : bulk compressibility of porous medium at constant fluid pressure [L t2 M−1] c s : bulk compressibility of rock matrix [L t2 M−1] c u : uniaxial compressibility of the porous medium [L t2 M−1] C : aqueous concentration [M L−3] D : hydrodynamic dispersion [L2 t−1] D w : diffusion coefficient in open water [L2 t−1] E : energy [E] F : fluxibility [M L−3 t−1] g : gravitational acceleration [L t−2] G : shear modulus, [M L−1 t−2]. H : specific enthalpy [E M−1] k : intrinsic permeability [L2] k : reference intrinsic permeability [L2] k r : relative permeability [dimensionless] K : thermal conductivity [E t−1 L−1 T−1] L : characteristic length or distance [L] M : mass [M] P : pressure [M L−1 t−2] P c : capillary pressure [M L−1 t−2] q : volumetric flow rate per unit area (volume flux, specific discharge or Darcy velocity) [L t−1] R : general source/sink term for mass, heat, or chemical reactions [variable] s s : specific storage [L−1] S : volumetric saturation [L3 L−3, dimensionless] t : time [t] T : temperature [T] u : displacement vector [L] U s : shear displacement [L] v : average linear velocity (seepage velocity) [L t−1] X : mass fraction H2O, NaCl, or CO2 in an H2O-NaCl-CO2 mixture [dimensionless] z : elevation above a datum, vertical Cartesian coordinate, or depth [L] z g : elevation parallel to the direction of gravity [L] α : dispersivity [L] α e : effective stress coefficient, [dimensionless] α T : porous medium linear thermal expansivity [T−1] β : bulk fluid compressibility [L t2 M−1] θ : potential per unit mass [E M−1] λ : coefficient of friction [dimensionless] μ : dynamic viscosity [M L−1 t−1] v : Poisson’s ratio [dimensionless] ρ : density [M L−3] σ : stress [M L−1T−2] σ eff : effective normal stress σ nref : effective normal stress to a fracture τ : tortuosity [dimensionless] φ : porosity [dimensionless] φ e : effective porosity [dimensionless] Φdil : shear dilation angle ( ∧ ) : indicates increase or decrease in a quantity (-) : indicates a nondimensionalized quantity * ### Subscripts f : refers to the fluid mixture in place (either a single phase or a two-phase mixture) l : refers to liquid m : refers to the porous medium r : refers to the rock v : refers to vapor (steam) : refers to an initial state

Fluid inclusion study of the Nannihu giant porphyry Mo–W deposit, Henan Province, China: Implications for the nature of porphyry ore-fluid systems formed in a continental collision setting

The Nannihu Mo–W deposit, located in the Henan Province of China, is a giant porphyry deposit formed in the Qinling Orogen during the Jurassic continental collision between the North China and Yangtze Cratons. Mo–W mineralization is associated with the Nannihu porphyritic monzogranite, occurring as numerous stockwork veinlets in the altered wallrocks and the causative porphyry. Both the porphyry stock and wallrocks underwent intense hydrothermal alteration, ranging outwardly from potassic to phyllic alteration, and to carbonation zones with increasing distance from the intrusion. The hydrothermal ore-forming process can be divided into four stages characterized by veinlets, from early to late: (1) quartz+potassic feldspar±molybdenite±pyrite; (2) quartz+molybdenite veins containing minor pyrite and chalcopyrite; (3) quartz+polymetal sulfide; and (4) quartz+carbonate+fluorite. Most of the ores are formed during stages 2 and 3.Four types of fluid inclusions (FIs) are distinguished in this study based on petrographic and microthermometric criteria, i.e. pure CO2, NaCl–H2O, CO2–H2O and daughter mineral-bearing fluid inclusions. All of the four types of FIs can be observed in the hydrothermal quartz formed in stages 1, 2 and 3; while the stage 4 minerals contain only NaCl–H2O fluid inclusions. Fluid inclusions of stage 1 are mainly homogenized between 350 and 460°C, with salinities ranging from 5.7 to 17.9wt.% NaCl equiv. The stage 2 FIs yield homogeneous temperatures of 300–380°C and salinities of 3.5–16.9wt.% NaCl equiv. FIs of stage 3 are homogenized between 250 and 370°C, with salinities of 1.8–14.3 and 28.6–39.1wt.% NaCl equiv. FIs of stage 4 are homogenized at temperatures of 115 to 265°C, yielding salinities of 0.5 to 1.2wt.% NaCl equiv. Daughter minerals, such as halite, chalcopyrite and some unknown minerals, are frequently present in stage 3 FIs, which probably represent a reducing and oversaturated fluid-system resulting from fluid-boiling. The daughter mineral-bearing FIs coexist with vapor- and liquid-rich NaCl–H2O FIs that have contrasting salinities. These FIs are homogenized in divergent ways at similar temperatures, suggesting that fluid boiling took place in stages 2 and 3. The estimated pressures range from 70 to 270MPa in stage 1, through 30–150MPa in stage 2, to 30–85MPa in stage 3, corresponding to a depth of no less than 3km. In other words, the ore-forming fluids are characterized by high temperature, high salinity, high fO2 and high CO2 content; and fluid-boiling resulted in CO2 release, fO2 decrease and ore mineral precipitation. We suggest that the CO2-rich fluid is a distinctive feature of porphyry systems developed in continental collision setting, in transitional compressional to extensional regime, contrasting to the CO2-poor NaCl–H2O fluids observed in volcanic arcs.