Breccia Ores Research Articles

Distribution of In, Sn, Ga, Ge, and other critical metals in sulfide ores from epithermal listvenite-associated Badovc Pb–Zn–Sb–Ni deposit (Kosovo): Insights from mineralogy and geochemistry

This work presents a mineralogical and geochemical study of sulfide ores from the epithermal listvenite-associated Badovc Pb–Zn–Sb–Ni deposit, which is located in the central part of the Kizhnica-Hajvalia-Badovc ore field, in the Trepça Mineral Belt (TMB) in Kosovo. Badovc is an example of one of many base-metal Pb–Zn–Ag deposits associated with the Serbo-Macedonian metallogenic province. There are three types of ores, the first two associated with polymetallic epithermal IS veins (massive-banded Pb–Zn–Sb and rhodochrosite-stibnite breccia) and disseminated ores associated with listvenites, which are hydrothermally altered mafic and ultramafic rocks. The mineralogy of these ores was described using EPMA in combination with reflected and transmitted light microscopy. The mineralogy of massive-banded Pb–Zn–Sb and rhodochrosite-stibnite breccia ores is relatively limited: sphalerite + rhodochrosite-siderite + pyrite/marcasite ± Pb–Sb sulfosalts ± stibnite. Listvenite Pb–Zn–Sb–Ni ores are more mineralogically variable due to the multi-stage formation of these rocks and the overprint of polymetallic mineralization. Apart from typical base-metal sulfides such as sphalerite, pyrite, galena, and chalcopyrite, the listvenite ores contain Fe–Mn carbonates, quartz, and Ni–Fe ± As ± Sb association (gersdorffite, ullmannite, millerite, and Ni–Fe thiospinels), Sn minerals (stannite and cassiterite). The LA-ICP-MS technique was used to determine critical metals occurring as minor and trace elements and substitution mechanisms in sphalerite, pyrite, stibnite, chalcopyrite and stibnite. The main critical metals, such as In, Sn, Ga, and Ge, are hosted by sphalerite in all types of ores. The highest concentrations of tin in sphalerite are observed in massive-banded Pb–Zn–Sb ores, which substitutes within the 3Zn2+ ↔ 2(Cu, Ag)+ + Sn4+ mechanism. The highest concentrations of indium are observed in sphalerites from listvenites, indicating the 2Zn2+ ↔ Cu+ + In3+ substitution. Low-temperature sphalerites from rhodochrosite-stibnite breccia exhibit elevated concentrations of Ga, Ge, and Ag, which incorporate into the structure through 2Zn2+ ↔ (Ag, Cu)+ + Ga3+, and 3Zn2+ ↔ 2(Cu, Ag)+ + Ge4+ mechanisms. The specific crystallization temperatures using GGIMFis for sphalerite are: 248–332 °C for massive-banded Pb–Zn–Sb ores, 208 °C for rhodochrosite-stibnite breccia, and 2112–344 °C for listvenite Pb–Zn–Sb–Ni ores. Additionally, stibnite from Badovc exhibits substitutions such as As3+ ↔ Sb3+ and (Cu+ + Ag+) + Pb2+ ↔ Sb3+ + □, and can incorporate various monovalent elements other than copper, including Ag+ and Tl+. Studies of epithermal listvenite-associated Badovc Pb–Zn–Sb–Ni deposits suggest that similar deposits spread across the Balkans may hold considerable prospectivity.

Magmatic‐hydrothermal evolution and mineralization mechanisms of the Wangjiazhuang Cu (‐Mo) Deposit in Zouping Volcanic Basin, Shandong Province, China: Constraints from Fluid Inclusions

AbstractWangjiazhuang Cu (‐Mo) deposit, located within the Zouping volcanic basin in western Shandong Province, China is the only one with economic value found in the area so far. In order to expound the metallogenetic characteristics of this porphyry‐like hydrothermal deposit a detailed fluid inclusion study has been conducted employing the techniques of representative sampling, fluid inclusion petrography, microthermometry, Raman spectroscopy, La‐ICP‐Ms analysis of single fluid inclusions, as well as cathode fluorescence spectrometer analysis of host mineral quartz. The deposit contains mainly two types of orebodies, i.e. veinlet‐dissemination‐stockwork orebodies in the K‐Si alteration zone and pegmatitic‐quartz sulfide veins above them. In addition, minor breccia ore occurs locally. Four types of fluid inclusions in the deposit and altered quartz monzonite are identified: L‐type one‐ or two‐phase aqueous inclusions, V‐type vapor‐rich inclusions with V/L ratios greater than 50‐90%, D‐type multiphase fluid inclusions containing daughter minerals or solids and S‐type silicate‐bearing fluid inclusions containing mainly muscovite and biotite. Ore petrography and fluid inclusion study has revealed a three‐stage mineralization process driven by magmatic‐hydrothermal fluid activity as follows. Initially a hydrothermal fluid separated from the parent magma infiltrated into the quartz monzonite, resulting in its extensive K‐Si alteration as indicated by silicate‐bearing fluid inclusions trapped in altered quartz monzonite. This is followed by the early mineralization, the formation of quartz veinlets and dissemination‐stockwork ores. During the main mineralization stage due to the participation and mixing of meteoric groundwater with the magmatic‐sourced hydrothermal fluid the cooling and phase separation caused deposition of metals from the hydrothermal fluids. As a result the pegmatitic‐quartz sulfide‐vein ores formed. In the late mineralization stage, decreasing in fluid salinity has led to the formation of L‐type aqueous inclusions and chalcopyrite‐sulfosalt ore. Coexistence of V‐type and D‐type inclusions and their similar homogenization temperatures but different homogenization modes suggest that phase separation or boiling of the ore‐forming fluids once took place during the early and the main mineralization stages. The formation P‐T conditions of S‐type inclusions, and the early and the main mineralization stages are estimated as ca. 156 ∼ 182 MPa and 450 ∼ 650 °C, 350‐450 °C, 18‐35 MPa and 280‐380 °C, 8‐15 MPa, respectively based on the microthermometric data of the fluid inclusions formed at the individual stages.

Percolation of sulfide liquid through semi-consolidated silicate cumulates: Textural evidence from breccia ores in the Kalatongke Cu-Ni sulfide deposit, NW China

The Kalatongke Cu-Ni sulfide deposit is an important Ni producer in China and contains abundant breccia ores which are especial in that the silicate fragments enclosed within the sulfide matrix have similar mineral assemblages to the host norite body. Using a combination of microbeam X-ray fluorescence (μ-XRF) and Tescan integrated mineral analyzer (TIMA) mapping, and 3D morphology by high-resolution X-ray computed tomography (HRXCT), we show that the breccia ores are of magmatic origin, as there are no foliation and fabrics of silicate fragments in the sulfide matrix. The 3D morphology of the breccia ores reveal that large silicate fragments are continually connected, whereas small silicate fragments are sub-spheric to spheric with sphericity values close to 1 and commonly rimed by magnetite. All these textures can be explained by that semi-consolidated silicate cumulates were percolated by sulfide liquid from replenished sulfide-bearing magma pulse in the magma conduits. The sulfide liquid from the replenished magma may have accumulated to form a sulfide pool overlying the semi-consolidated cumulates. Due to its high density, the sulfide liquid in the pool could percolate downward and infill the fracture network in the semi-consolidated cumulates, forming sulfide networks in the breccia ores. The sulfide liquid may also trap the interstitial, silicate melts on its way downward throughout the semi-consolidated cumulates, forming small sub-spheric to spheric silicate fragments in the breccia ores. Such a process revealed by the texture of breccia ores indicates that replenished magma pulses and degrees of percolation of sulfide liquid through semi-consolidated cumulates essentially control the distribution of ore bodies in the Kalatongke deposit.

The effect of platinum-group minerals on differentiation of platinum-group elements in magmatic sulfide deposits: Evidence from the Cu-Ni-PGE deposits in the Yangliuping area of the Emeishan large igneous province, SW China

Platinum-group minerals (PGM) are important host phases for platinum-group elements (PGE) in magmatic sulfide deposits. Recent studies have demonstrated that some PGM, such as sperrylite, can crystallize early from sulfide liquids. It is important to determine whether and how these PGM particles affect the enrichment and differentiation of PGE in Cu-Ni-PGE deposits. The magmatic sulfide deposits in the Yangliuping area (mainly consisting of the Yangliuping deposit and Zhengziyanwo deposit) are the largest Cu-Ni-PGE deposits in the Emeishan large igneous province, SW China. Primitive-mantle normalized PGE patterns and fractional crystallization modelling show that massive ores in the Yangliuping deposit are enriched in Pd and Pt. In contrast, massive ores, breccia ores and Cu-rich ores in the Zhengziyanwo deposit are depleted in Pt. Scanning electron microscopy (SEM), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), focused ion beam (FIB) and transmission electron microscopy (TEM) were used to constrain the occurrence of PGE in the massive ores from the two deposits. Mass balance calculation shows that <7% of Ir, Rh and Pt occur in base metal sulfides (BMS, mainly pyrrhotite, pentlandite and chalcopyrite) as solid solution in both the Yangliuping and Zhengziyanwo massive ores. 17% and 91% Pd are present in solid solution within BMS in the Yangliuping and Zhengziyanwo massive ores, respectively. In the Yangliuping massive ores, PtAs2 and Pd-PGM particles were commonly found within BMS crystals, and Ir-Rh-(Pt) sulfarsenides enclosed in cobaltite-gersdorffite solid solution (CGSS) are enriched in Pt. In contrast, in the Zhengziyanwo massive ores, no PtAs2 particles and fewer Pd-PGM particles were found, and Ir-Rh-(Pt)AsS particles enclosed in CGSS are poor in Pt. The distribution, mineralogy and microstructures of Ir-Rh-(Pt)AsS, PtAs2 and Pd-PGM particles in both the Yangliuping and Zhengziyanwo deposits suggest that they mainly crystallized from sulfide liquids or formed from Pd-Pt-semimetal-rich droplets. We suggest that the incorporation of Pd-PGM and PtAs2 particles into MSS cumulates led to the enrichment of Pd and Pt in the Yangliuping massive ores. In the Zhengziyanwo deposit, early fractional crystallization of PtAs2 reduced the Pt content in sulfide liquids and resulted in the formation of Pt-depleted sulfide ores and low-Pt Ir-Rh-(Pt)AsS particles, but no Pt-rich sulfide ores have been found to date. As a result, the role of PGM particles should be considered when using PGE to trace the formation process of Cu-Ni-PGE deposits. This study also provides additional evidence that the behavior of Pt in sulfide liquids is influenced by thermodynamic conditions and As, and suggests a potential for Pt-rich sulfide ores exploration in the Zhengziyanwo deposit.

Classification of Polymetallic Ore-Forming Processes and Transitional VMS–SEDEX–MV-type: the Example of the Giant Ozernoe Deposit in Transbaikalia, Russia

This article discusses the general classification approaches and key features of different families of polymetallic deposits, with particular attention to the largest in Eurasia Ozernoe polymetallic deposit located in Western Transbaikalia and thoroughly explored 50 years ago. The main groups (or families) of polymetallic deposits in the English-language literature are identified by brief names: volcanogenic massive sulphide (VMS), sedimentary exhalative (SEDEX), and Mississippi Valley type (MVT). Within these three families of deposits, there are many additional types/subtypes, a large number of which are mostly due to the incompleteness and inconsistency of accumulated knowledge on the genesis of polymetallic deposits. Overall, all Pb–Zn(Ag,Cu) deposits—both those that are considered syngenetic, forming on and near the seafloor (VMS and SEDEX), and epigenetic low-temperature ones (MVT)—demonstrate a wide range of features that distinguish and bring together these families. This also applies to the types and subtypes of mineral deposits identified within them. One of the most complex objects for geological–genetic classification is the Ozernoe deposit studied by the authors, which, in terms of the nature of the host rocks, is intermediate between the end members of all three families: SEDEX, VMS and MVT. The deposit is localized in volcanic–carbonate–terrigenous rocks of the Cambrian Oldynda formation, but the age and stratigraphic affiliation of the ore-bearing series remain a matter of debate. The Ozernoe deposit is a combination of massive sulfide and siderite ore beds, ore breccia horizons, low-carbonate aleuropelite members, limestones, fine detrital tuffites, lavas, and tuffs. The sulfide bodies are confined to several stratigraphic levels, and the main productive unit thickness reaches 230 m. The thickness is comprised of 12 mineral lodes, a series of stratified ore bodies separated by gangue layers of sedimentary and volcaniclastic rocks. The primary ore minerals are pyrite, sphalerite, and galena, while the minor minerals include magnetite, chalcopyrite, marcasite, tetrahedrite, and arsenopyrite. There are two main theories regarding the origin of the ore: volcanogenic–sedimentary and hydrothermal–metasomatic. The hydrothermal–sedimentary theory remains the prevailing hypothesis, but there are many indications that epigenetic hydrothermal–metasomatic and dynamic metamorphic processes have contributed to the formation of the deposit. These include the appearance of sulfide–quartz and quartz–carbonate–sulfide veins and vein zones in fine-grained “layered” ores, with large crystalline sphalerite and galena; multiple signs of ore recrystallization, including the formation of pyrite porphyroblasts and arsenopyrite metacrystals; and the formation of solid pyrrhotite and pyrrhotite–magnetite ores with a lenticular-striped, gneissic structure. These observations suggest that different processes, both hydrothermal–sedimentary and metamorphogenetic–metasomatic, were involved in the formation of the Ozernoe deposit. In other words, primary hydrothermal–sedimentary ores were redeposited by late hydrothermal solutions. Nevertheless, many issues concerning the genesis of the Ozernoe deposit remain unresolved.

Geochemistry of magnetite from the Mamupu Cu polymetallic deposit, Yulong belt, Tibet: Implications for magnetite genesis, stages and mechanism of formation

The Mamupu copper polymetallic deposit is characterized by multistage magnetite, but the genesis and fluid evolution process of this deposit are still obscure. Three types of magnetite were identified in Mamupu based on comprehensive textural observations and paragenesis. Mag1 occurs as subhedral to euhedral crystals, and smooth Mag1a and porous Mag1b can be distinguished under Backscattered Electron (BSE). Mag2 is characterized by 120° triple junction textures and has been replaced by hematite. Mag3 is commonly replaced by hydrothermal fluids and exhibits well-developed oscillatory zoning and core (Mag3a)-rim (Mag3b) textures. The geochemistry of Mamupu magnetite suggests that they are of hydrothermal origin. Mag1 has undergone extensive fluid-rock interactions, whereas the sharp contacts with Mag1a and Mag1b and the microporosity of Mag1b imply that the Mag1b was generated by the coupled dissolution reprecipitation of the Mag1a grains. This process may be triggered by low-temperature and high-salinity fluid produced by intensive water-rock interaction between ore-bearing magmatic-hydrothermal fluid and carbonate surrounding rock of the Jiaoga Formation. The 120° triple junction textures of Mag2 indicate that it was formed during a fluid-assisted recrystallization process, and Mag2 replaced by hematite represents the increase in oxygen fugacity. From Mag3a to Mag3b, the contents of V and Mn increased while the contents of chalcophile elements decreased, suggesting a decrease of oxygen fugacity and the precipitation of sulfide, which represents the beginning of the sulfide stage. Moreover, petrography and geochemistry data of magnetite represented that the breccia ore of Mamupu belongs to skarn mineralization. The geochemical characteristics of magnetite show that Cu-Au and W-Mo in Mamupu precipitated in different stages, representing the transformation from a relatively oxidized environment in the early stage to a relatively reduced environment in the late stage. These results reveal that trace elements in magnetite can be utilized to define the genesis and evolution of the skarn deposit. In addition, it can also restrict the precipitation mechanism of ore-forming elements in the deposits. However, detailed textural observations should be carried out before experimental research.

Localization features of pyrite-polymetallic oresof the Tushkanikhinskoye deposit (Rudny Altai)

The Tushkanikhinskoye deposit is confined to the Devonian basalt-bearing rhyolite calcareous-siliceousterrigenous formation, which is represented by sedimentary, volcano-sedimentary, sedimentary-volcanogenic, pyroclastic, volcanic rocks of felsic and basic composition, as well as their subvolcanic equivalents. Felsic volcanogenic rocks show signs of ignimbrites. Primary pyrite-polymetallic ores with an uneven distribution of the main sulfi sphalerite, pyrite, galena, and chalcopyrite have been identified. The presence of collomorphic, framboidal and granoblastic pyrite in the ores, as well as the presence of sedimentary breccia ores with sulfi in clasts and matrix advocates for the hydrothermal-sedimentary origin of the ores. The ore bodies represent destroyed hydrothermal structures, so-called "ore hills".

Polymetallic Sulfide–Quartz Vein System in the Koudiat Aïcha Massive Sulfide Deposit, Jebilet Massif, Morocco: Microanalytical and Fluid Inclusion Approaches

The Koudiat Aïcha Zn-Cu-Pb deposit (3–Mt ore @ 3 wt.% Zn, 1 wt.% Pb, 0.6 wt.% Cu) in the Jebilet massif (Morocco) comprises stratabound lenticular orebodies and crosscutting sulfide-bearing quartz ± carbonate veins in the lower Carboniferous Sarhlef volcano sedimentary succession. The veins are characterized by abundant pyrrhotite, sphalerite, subordinate chalcopyrite and galena and rare Ag and Au minerals. The stratabound massive sulfide ores are attributed to a “VMS” type, whereas the origin of the sulfide–quartz ± carbonate veins remains poorly understood. New mineralogical and microanalytical data (SEM, EPMA and LA-ICP-MS) combined with fluid inclusion results point to two-stage vein formation. The early stage involved C–H–O–N Variscan metamorphic fluids which percolated through fractures and shear zones and deposited pyrite at &gt;400 °C, followed by the formation of pyrrhotite and sphalerite (300 ± 20 °C) in quartz veins and in banded and breccia ores. The pyrrhotite–sphalerite mineralization was overprinted by aqueous brines (34 to 38 wt% eq. NaCl + CaCl2) that precipitated carbonate and Cu-Pb sulfides (±Ag-Au) at ~180–210 °C through mixing with low-salinity fluids during tectonic reworking of early-formed structures and in late extension fractures. The latter ore fluids were similar to widspread post-Variscan evaporitic brines that circulated in the Central Jebilet. Overlapping or successive pulses of different ore fluids, i.e., metamorphic fluids and basinal brines, led to metal enrichment in the quartz–carbonate veins compared to the massive sulfide ores. These results underscore that even a single deposit may record several distinct mineralizing styles, such that the ultimate metal endowment may be cumulative over multiple stages.

Paleoproterozoic gold deposits at Alta Floresta Mineral Province, Brazil: two overprinted mineralizing events?

Abstract Large gold provinces commonly show complicated mineralization histories, and the Paleoproterozoic Alta Floresta, one of Brazil's most exciting Au–Cu mineral provinces, is a good example. The current models defined four deposit types, all connected to a single (1.88–1.75 Ga) magmatic–hydrothermal event. However, long Province history, diverse geodynamic environment and older ages of Type-1mineralization weaken the single metallogenic event and enable the hypothesis of overprinted mineral events. By scale-integrated analyses, we revise the tectonic–geological context, structural–hydrothermal alterations and chlorite–white mica geothermobarometry and propose the Type-1 as an older, granitoid-hosted orogenic mineralization, with subsequent overprinting by the magmatic–hydrothermal event. The older orogenic gold event developed orogenic gold deposits on WNW-trending shear zones in the Peixoto de Azevedo domain granitic–gneiss rocks. Phengite, biotite and chlorite–carbonate phyllonites (3.3–6.1 kbar, 300–420°C) host fault-fill quartz veins (pyrite–chalcopyrite–magnetite–pyrrhotite–gold–Bi–Ag tellurides). Mg-rich chlorite–phengite is the main alteration footprint for this mineralization type. A younger magmatic–hydrothermal event in the Juruena magmatic-arc rocks produced Fe-rich chlorite–white mica alteration zones (0.6–4.6 kbar, 120–380°C) and disseminated and stockwork–breccia ore (pyrite–chalcopyrite–gold–molybdenite–Ti minerals–allanite) in porphyry–epithermal deposits. Where the younger mineralization overprints the older, phyllic alteration destroyed the phengite orogenic gold phyllonite S n +1 foliation. The ages of two pyrite populations (1979 and 1841 Ma) in the older fault-fill veins and molybdenite in late fractures (1805–1782 Ma) or disseminated in the c. 1.79 Ga syenogranite porphyry suggest more than two episodes of mineralization. These two events differ in their alteration styles, P–T conditions and structural, mineralogical and textural ore styles. The multiscale approach sheds light on the relationships between the various mineralization events, allowing a new explorational potential within the province. Supplementary material: Chlorite and white mica complete chemical composition data and other characteristics of the studied deposits are available at https://doi.org/10.6084/m9.figshare.c.6056324

Timing and ore genesis of the Ciweigou low-sulfidation epithermal gold deposit in the Yanbian Cu-Au district, NE China

The Ciweigou low-17 sulfidation epithermal Cu-Au mining district, NE China, is hosted by Early Cretaceous andesite of the Jingouling Formation. From bottom to top (not explored below the 100 m level), the ore bodies consist of gold-bearing quartz veins, gold-bearing quartz-calcite veins, and calcite veins and the sides are stockwork veins and hydrothermal breccia ore bodies. Five mineralization stages are distinguished: (I) pyrite-sericite, (II) quartz-calcite, (III) grey quartz, (IV) milky quartz-adularia and (V) late carbonate. Au-bearing minerals deposited in stages II and III. Hydrothermal alteration is composed of an inner silicic-pyritic zone, intermediate zone of quartz-sericite-adularia, outer zone of quartz-chlorite-epidote and upper zone of calcite. Systematic fluid inclusion petrography shows that two-phase vapour-rich and liquid-rich inclusions are the dominant fluid inclusions types in the quartz and calcite veins, suggesting that the ore-forming fluids belong to a moderate- to low-temperature (140 °C−320 °C) and low-salinity (0 wt%−14 wt% NaCl-eqv.) H2O-NaCl-CO2 system. HO isotopes (δ18OH2O = -14.0 ‰ to −4.9 ‰ and δD = −123.4 ‰ to −88.1 ‰) indicate that the ore-forming fluids likely originated from mixed fluids driven by residual andesitic magmatic fluid. The precipitation mechanisms are mixing and major fluid boiling. The comprehensive geological and isotopic characteristics show that the Ciweigou deposit is a low-sulfidation epithermal deposit. Six pyrite samples from stages I and II yielded a Rb-Sr isochron age of 102.6 ± 2.2 Ma (MSWD = 1.19), consistent with other low-sulfidation epithermal gold mineralization ages in the Yanbian district and Lesser Xing'an Range. The timing of the Ciweigou gold mineralization at ∼103 Ma postdates the eruption of andesitic magma (106.4 ± 2.1 Ma, zircon U–Pb) and granodiorite porphyry (106.6 ± 1.2 Ma, zircon U–Pb) and diorite porphyry (107.8 ± 1.8 Ma, zircon U–Pb) emplacement, suiting in an extensional environment attributed to the rollback of the subducting Paleo-Pacific Plate.

A Mississippi Valley–type Zn-Pb mineralizing system in South China constrained by in situ U-Pb dating of carbonates and barite and in situ S-Sr-Pb isotopes

AbstractThe ages of Zn-Pb deposits are exceptionally challenging to determine owing to the lack of suitable mineral chronometers and techniques. Here we present the first result for in situ LA-ICP-MS U-Pb dating of carbonates and barite from a Mississippi Valley– type (MVT) Zn-Pb deposit in South China. Hydrothermal dolomite in close textural and paragenetic association with Zn-Pb sulfides, and calcite and barite cement from the breccia ores, yield ages of 473.4 ± 2.7 Ma and 368.7 ± 3.1 Ma, respectively. Together with new in situ S-Pb-Sr isotope values, these data reveal an epigenetic Zn-Pb mineralization history, agreeing well with a model involving basinal brine accumulation and MVT Zn-Pb sulfide precipitation. Because carbonate is a common mineral in Zn-Pb deposits worldwide, and other minerals in such deposits suitable for isotope dating are generally absent, in situ U-Pb dating of gangue carbonates opens a new window for better defining the ore genesis of this globally important Zn-Pb deposit type and for tracking hydrothermal fluid flow in sedimentary basins.

Sulfide Ore Formation of the Kalatongke Ni-Cu Deposit as Illustrated by Sulfide Textures

Abstract The Kalatongke magmatic Ni-Cu deposit features high Ni-Cu grades compared with other Ni-Cu deposits in the Central Asian orogenic belt. The sulfides, mainly hosted by olivine norite and gabbronorite, are characterized by high Cu/Ni ratios. There is wide variety of textural relationships in the mineralized rocks, including globular, sulfide matrix, emulsion, disseminated, net-textured, and semimassive to massive textures. Quantitative textural measurements reveal that more than 65 vol % of the total sulfide volume in disseminated ore (defined as containing 4–10 vol % sulfide) and more than 90 vol % of the total sulfide volume in net-textured ore (typically 16 vol % sulfide) are hosted in few interconnected networks with equivalent sphere diameters (ESDs) larger than 6 mm. This illustrates that sulfide coalescence is a critical process. The remaining sulfide blebs define two groups of log-linear particle size distribution (PSD), i.e., a finer group (ESD of 0.080–&amp;lt;0.529 mm) and a coarser group (ESD of 0.529–4.084 mm). The PSD of the finer group differs slightly among different types of mineralization. The origin of this group of sulfides is attributed to sulfide nucleation simultaneously with crystallization of the olivine-orthopyroxene-plagioclase phases from the ore-forming magma in the current magma chamber. The PSD of the coarser group from net-textured ores is parallel to that from the disseminated ore but has lower intercept values. Modeling results show that aggregation of ~40–70% sulfide blebs of different grain size from the disseminated ore into the networks can generate the coarser group sulfide PSD of net-textured ore. In addition, monosulfide solution (MSS, pyrrhotite component)-enriched sulfide globules are commonly located close to sulfide matrix ore breccias and emulsion-textured ores, rimming the net-textured and massive orebodies. These globules are different from the sulfide component that was in equilibrium with the mafic magma, suggesting they were formed by mechanical remobilization of a cumulus MSS-enriched component from a previously segregated and partially crystallized sulfide pool. These observations, combined with the ubiquitous chilled margin xenoliths in the high-grade ores, suggest that the Kalatongke deposit was the result of voluminous magma flow through the current location accompanied by sulfide reworking and percolation. All these textural characteristics could be explained by emplacement within a laterally propagating bladed dike. Moreover, the deformation recorded in the emulsion-textured and massive ores suggests the fault system remains active during magma solidification, driving downward migration of sulfide from the sulfide pool at magmatic temperature to form vein-type massive ore. We suggest that the Kalatongke deposit formed by magma pulses injecting into the current location and that the tectonic movement remains active during the solidification of the intrusion. The syntectonic emplacement model, which may be a common feature in the Central Asian orogenic belt Ni-Cu deposits, indicates that the fault systems beneath the intrusion are of great exploration interest for high-grade ores.

Compositions and Ni-Cu-PGE Tenors of Nova-Bollinger Ores with Implications for the Origin of Pt Anomalies in PGE-Poor Massive Sulfides

Abstract The Nova-Bollinger Ni-Cu-platinum group element (PGE) deposit in the Fraser zone of the Albany-Fraser orogen consists of two main orebodies, Nova and Bollinger, hosted by the same tube-shaped intrusion but having distinctly different Ni tenors of around 6.5 and 4.8 wt %, respectively. Nova is also higher in Pd, but Cu and Pt tenors are similar. Both deposits have very low PGE tenors, with average Pd concentrations of 110 ppb in massive sulfide at Bollinger and 136 ppb at Nova. The Nova and Bollinger orebodies show relatively little internal differentiation overall on deposit scale but show strong differentiation into chalcopyrite-rich and chalcopyrite-poor regions at a meter scale. This differentiation is more prevalent at Nova, where massive sulfide-filled vein arrays are more extensively developed, and in massive ores, particularly veins, than in net-textured ores. Net-textured and disseminated ores have on average Ni and Cu grades and tenors similar to those of massive, semimassive, and breccia ores in the same orebody but a smaller range of variation, largely due to a more limited extent of sulfide liquid fractionation and higher average concentrations of Pt and Pd than adjacent massive ores. Unusually for differentiated magmatic sulfides, there is no systematic positive correlation between Pt, Pd, and Cu. A partial explanation for the lack of a Pd-Cu correlation is that Pd was partitioned into peritectic pentlandite in the middle stages of sulfide liquid solidification. This explanation is not applicable to Pt, as Pt characteristically forms its own phases rather than residing in base metal sulfides. PGE tenors are very low in both orebodies, very similar to those observed in other Ni-Cu-Co sulfide ores in orogenic settings, notably the Savannah and Savannah North orebodies. This depletion is attributed to sulfide retention in the mantle source of the parent magmas rather than to previous fractional extraction of sulfide liquid in staging chambers or feeder networks. The higher Ni and Pd tenors at Nova are attributed to reworking and upgrading of precursor sulfide liquid originally deposited upstream at the Bollinger site. Replicate analyses of multiple jaw-crusher splits returned highly variable Pt and Au assays but much smaller relative errors in the other PGEs. The poor Pt and Au reproducibilities are attributed to nugget effects, explicable by much of the Pt and Au in the samples being present in sparse Pt- and Au-rich grains. This is principally true for Pt in massive rather than disseminated ores, accounting for a strong contrast in the distribution of Pt/Pd ratios between the two ore types. Numerical simulation suggests that Pt is predominantly resident in Pt-rich platinum group minerals with grain diameters of 100 µm or more and that at the low (&amp;lt;100 ppb) concentrations in these ores, this results in most assays significantly underreporting Pt. This is likely to be true in other low-PGE ores, such that apparent negative Pt anomalies in massive ores may in such cases be attributable to sampling artifacts.

Protracted mafic magmatism and two-stage mineralization of the Kalatongke Cu-Ni sulfide deposit in the Central Asian Orogenic Belt

The Kalatongke Cu-Ni sulfide deposit in the Central Asian Orogenic Belt (CAOB) is hosted by the early Permian mafic intrusions. After conducting a detailed field survey, we found that the massive sulfide ores and network olivine gabbro were emplaced separately into the dominant sulfide-barren mafic suite. Secondary ion mass spectrometry (SIMS) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) were performed for zircon U-Pb dating to determine the ages of rocks derived from the sulfide-rich suites and adjacent sulfide-barren suites. The results revealed that the U-Pb ages of olivine gabbro with network ore, gabbro with globular ore and breccia ore are 276.0 ± 1.1, 272.4 ± 0.9 and 271.9 ± 1.3 Ma, respectively. Biotite diorite in the Y1 intrusion, biotite gabbro and biotite norite in the Y2 intrusion presented with ages of 287.4 ± 1.1, 281.7 ± 3.0 and 286.7 ± 1.1 Ma, respectively. Combined with the published data, our findings demonstrated that the Kalatongke sulfide deposit experienced two stages of magma replenishment, lasting at least 16 Myr (287–271 Ma). The sulfide-rich magmas were most likely transported upward from the staging chamber via magma overpressure attributable to considerable tectonic compressive stresses. It could be proposed that the sulfide-rich magmas were derived from a strongly evolved magma chamber, whereas the sulfide-barren mafic suite was related to the emplacement of a weakly evolved magma in the same or a related plumbing system.

Decoupling of Au and As during rapid pyrite crystallization

Abstract Gold (Au) is largely hosted by pyrite in a variety of hydrothermal systems, but the incorporation of Au into pyrite under disequilibrium conditions remains poorly understood. We integrate synchrotron X-ray fluorescence microscopy, electron backscatter diffraction, nanoscale secondary ion mass spectrometry, and laser ablation–multicollector–inductively coupled plasma–mass spectrometry to constrain the processes that sequester Au into zoned pyrite in the hydrothermal cement of breccia ores from the world-class Daqiao orogenic Au deposit, central China. Euhedral pyrite cores with oscillatory and sector zoning, variable δ34S values, and lower Au-As contents than the mantles are attributed to crystallization during oxidation of metal-depleted ore fluids with local variation in fluid conditions. The isotopically uniform colloform mantles are formed by pyrite crystallites separated by low-angle boundaries and are characterized by unusual decoupling of Au and As. Mantle formation is attributed to rapid disequilibrium precipitation from a metal-rich FeS2-supersaturated fluid. Incorporation of Au into the pyrite mantles was facilitated by abundant lattice defects produced by rapid nucleation. Gold-As–poor pyrite rims were deposited from an evolved ore fluid or other metal-depleted fluids. These results show that chemical variations recorded by fine layering within minerals can provide valuable insights into disequilibrium mass transfer and ore formation. The decoupling between Au and As in pyrite mantles indicates that As is not always a reliable proxy for Au enrichment in rapidly crystallized porous pyrite.

PETROLOGICAL CHARACTERISTICS OF CLASTIC SEDIMENTARY ROCKS FROM THE ST. BARBARA ORE MINE IN RUDE NEAR SAMOBOR

In the scope of this research, the petrographic and geochemical analyses of clastic sedimentary rocks from the St. Barbara, copper and iron ore mine in Rude near Samobor, have been made, aiming to classify and determine the provenance and environment of formation of clastic sedimentary rocks, as well as the influence of hydrothermal fluids on their properties. Eight samples were collected in total from different locations in the mine. Six of those samples have been studied in detail. The results showed structural and geochemical variability and uneven hydrothermal alteration intensity in the samples. Based on petrographic analyses, three rocks are classified as sublithoarenite, quartz arenite and quartz greywacke. Three of the samples are classified as ore breccia, ore sandstone, and ore silt-sandstone due to the pronounced hydrothermal alterations and ore mineralisation. Comprehensively, petrographic and geochemical analyses indicate that the source rocks of the investigated clastic sedimentary rocks were felsic (La/Sc = 0.9-6.2; Th/Sc = 1.3-2.4), most probably sedimentary, possibly resedimented rocks. The extent of source rock weathering was very high (Chemical Index of Alteration CIA = 52.1 - 81.3 %) and the geotectonic position of the sedimentary basin was very likely to be at the passive continental margin.

In-situ LA-ICP-MS trace element and oxygen isotope signatures of magnetite from the Yamansu deposit, NW China, and their significance

The Yamansu iron deposit is hosted in submarine volcanic rocks in the Aqishan–Yamansu belt of Eastern Tianshan, NW China. A geological cross-section for the Carboniferous strata in the ore district shows that ore bodies in the Yamansu deposit are hosted in andesitic crystal tuff of the third cycle of the Carboniferous Yamansu Formation. This indicates an association between mineralization and volcanism. The orebodies are strata bound and lensoid and generally share the occurrence state of the host rocks. Magnetite mineralization mainly occurs asbreccia ores, ores in the mineralized volcanic rocks, massive ores, and sulfide-rich ores according to their structures and sequences of formation. Trace element compositions of magnetite from various types of ores were determined by LA-ICP-MS. The dataset indicates thatdifferent types of magnetite havedistinct trace element contents correlated to their formation environments. Magnetite crystals from breccia ores have high Ti, Ni, V, Cr, and Co and low Si, Al, Ca, and Mg contents, indicating crystallization from a volcanic magmatic eruption, which is consistent with field evidence of coexisting altered volcanic breccia. Magnetite crystals from ores in the mineralized volcanic rocks have moderate Ti, Ni, V, Cr, and Co contents. In contrast, magnetite from massive ores and sulfide-rich ores have low concentrations of Ti, Cr, Ni, and V, high concentrations of Si, Al, Ca, and Mg, and evidence of hydrothermal magnetite. In-situ magnetite compositions imply a magmatic-hydrothermal process. Although δ18O values for magnetite grains fromYamansu vary (+ 1.3 to + 7.0‰), they all plot in the range field of volcanic iron deposits, and they also record a magmatic-hydrothermal process. The compositions of Yamansu magnetites are interpreted as controlled mainly by temperature, fluid, host rock buffering, oxygen fugacity, and sulfur fugacity. The metallogenic conditions of the Yamansu deposit changed from high temperature and low oxygen fugacity to low temperature and high oxygen fugacity. However, more fluid-rock reactions and higher sulfur fugacity were involved during the deposition of massive ores and sulfide-rich ores.

Paleo-tethys late triassic orogenic gold mineralization recorded by the Yidi’nan gold deposit, West Qinling, China

The Tongren-Xiahe-Hezuo polymetallic district in the West Qinling Orogen of central China has emerged as a promising new gold belt. However, significant debate exists as to whether the numerous Triassic intrusion-hosted lode gold deposits in the district represent intrusion-related or orogenic mineral systems. The Yidi’nan gold deposit is an example of a Triassic intrusion-hosted gold deposit endowed with an estimated resource of over 20 tonnes gold. The gold mineralization at Yidi’nan is fault-controlled and hosted by granite breccias associated with cataclastic zones. Its large size and intrusive host rocks make Yidi’nan an ideal site for attempting to resolve the origin of the intrusion-hosted gold systems in the West Qinling. Zircon U-Pb ages obtained as part of this study indicate that the ore-hosting quartz diorite pluton and a later dacite dike formed at 240.3 ± 2.5 and 239.3 ± 2.4 Ma. Hydrothermal sericite from fault gouge from main gold orebody returned much younger 40Ar/39Ar plateau and normal isochron ages of 220.21 ± 0.44 and 220.42 ± 7.69 Ma. Optical microscopy investigation revealed that the sericite coexists with gold-bearing sulfides, indicating that the sericite is coeval with gold mineralization. Our new age data reveal that gold mineralization at Yidi’nan postdated the Triassic magmatism by ca. 20 million years. Such a temporal framework is consistent with the observed geologic relationships, namely mineralized breccia ore crosscutting the quartz diorite host. Such evidence also suggests that the orogenic gold mineralization in West Qinling was not genetically linked to the Triassic magmatism associated with the subduction of the Paleo-Tethys Ocean. Instead, the formation of the Yidi’nan gold deposit appears to have been part of a mineralization event associated with a Late Triassic collisional event with the release of gold-bearing fluids possibly related to crustal thickening processes. High-angle reverse shear zones produced during ongoing continental collision probably facilitated the movement of hydrothermal fluids along major structures, eventually leading to the formation of plentiful orogenic gold deposits in West Qinling.

Ore breccias as a key to understanding the genesis of silver and gold deposits in Western Verkhoyanye

Ore breccias as a key to understanding the genesis of silver and gold deposits in Western Verkhoyanye

Ore formation at the Washan iron oxide–apatite deposit in the Ningwu Ore District, eastern China: Insights from in situ LA-ICP-MS magnetite trace element geochemistry

Iron oxide–apatite (IOA) deposits are an important type of iron deposit that may host large reserves of iron and other elements. The Washan deposit in the Ningwu Ore District is a classic giant IOA deposit hosted by porphyritic diorite. At Washan, four Fe mineralization stages have been identified with clear crosscutting relationships, forming four types of ores: disseminated ores, breccia ores, and magnetite–actinolite and magnetite–apatite–actinolite veins. Trace element concentrations and single-grain geochemical profiles of magnetite from the four Fe mineralization stages were obtained via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The geochemical profiles show consistent Ti, V, Mg and Al contents from cores to rims, indicating that magnetite might have crystallized quickly under relatively stable conditions in each stage. Compatible element (e.g., Co, V, Ni, and Cr) contents of the Washan magnetite are similar to those of magmatic Fe–Ti–V deposits, with high V and Ti contents, indicating a close magmatic link. Increasing Mg, Al, Mn, Ni and Ga contents and decreasing Cr content from early to late stages imply increasingly intense reactions between Fe-bearing fluids and country rocks (e.g., diorite and evaporites), which also suggests a magmatic-hydrothermal origin. We propose a new genetic model for ore formation at the Washan IOA deposit. First, an Fe-rich liquid, which may have formed via liquid immiscibility, ascended through the magma system, resulting in the disseminated ores and albite alteration in the porphyritic diorite. With cooling and crystallization of the magma, the intrusive rocks developed fractures and brecciation, which may have provided pathways for Fe-bearing fluids. After the breccia (or massive) ores formed, the pathways would have been quickly sealed by mineral precipitation. Continuous liquid immiscibility and magma crystallization may have produced similar fluids with more sedimentary material involved and its markers displayed. When the fluid pressure overcame the lithostatic pressure, the fractures that developed may have provided the necessary conduits for emplacement of the magnetite–actinolite and magnetite–actinolite–apatite veins. Subsequently, the magmatic-hydrothermal system might have remained active during cooling and differentiation, while pyrite–quartz and calcite veins formed.