JournalTOCs

Mineralium Deposita
Journal Prestige (SJR): 1.601

Citation Impact (citeScore): 4
Number of Followers: 4

Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1432-1866 - ISSN (Online) 0026-4598
Published by Springer-Verlag

[2469 journals]

Cu-sulfide mineralogy, texture, and geochemistry in the Tiegelongnan
porphyry-epithermal copper system, Tibet, China
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  Abstract: Abstract The Tiegelongnan porphyry-epithermal deposit (2089 Mt @ 0.53% Cu, 0.08 g/t Au) is host to a large variety of Cu-sulfide minerals, mainly chalcopyrite, bornite, covellite, digenite, enargite, and tennantite. We used LA-ICP-MS to investigate the trace element geochemistry of the Tiegelongnan Cu-sulfides, as well as pyrite, to understand the correlation between sulfides and trace elements, gold in particular, in the porphyry and epithermal systems. Porphyry mineralization consists of stage 1 chalcopyrite-pyrite ± molybdenite, stage 2 chalcopyrite-bornite, and stage 3 covellite. Epithermal sulfides form stage 4 pyrite-alunite, stage 5 digenite-bornite-chalcopyrite, and stage 6 enargite-tennantite ± tetrahedrite. Stage 2 chalcopyrite (S2 Ccp, median = 9.7 ppm Au) is the primary porphyry Au host, and stage 6 tennantite in alunite veins (S6 Tnt-s, median = 98.0 ppm Au) is the major epithermal Au host. These Au-rich sulfides formed under higher oxidation conditions, suggesting that a high oxidation state favors the incorporation of Au in Cu-sulfides. Gold contents in coeval chalcopyrite and bornite are positively correlated to temperature, and Au is enriched in chalcopyrite over bornite at low temperatures (< 350 ℃). Positive correlations between Au and As and Te in covellite and chalcopyrite result from the reaction of As3+ + (Au+/Ag+) + Te2− ↔ 4Cu+ + S2−. Epithermal chalcopyrite and bornite contain more As and Pd than that in porphyry stages, and high contents of As, Sn, Cd, Zn, Sb, Te, Au, and Bi in epithermal enargite and tennantite are likely the result of partitioning of these elements in sulfides at low epithermal temperatures. Epithermal overprinting likely leached Cu from earlier porphyry stage sulfides to precipitate high Cu-grade epithermal mineralization. The Cu-sulfides and related trace elements show a spatial distribution, potentially useful for the exploration of overprinted porphyry-epithermal systems.
  PubDate: 2022-06-01
Superimposed microstructures of pyrite in auriferous quartz veins as
fingerprints of episodic fluid infiltration in the Wulong Lode gold
deposit, NE China
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  Abstract: Abstract Complex microstructures of pyrite induced by superimposed deformation and fluid infiltration in lode gold deposits can record time-integrated physicochemical changes of ore-forming fluids. This study used a combination of techniques (EBSD, μ-XRF, EMPA, APT, and TEM) to characterize and decode the microstructures of pyrite in an optically homogeneous polymetallic sulfide veinlet of the Wulong lode gold deposit. The EBSD data show that the sulfide veinlet is composed of microstructurally heterogeneous pyrite grains in three generations, i.e., Py1, Py2, and Py3. The pyrite grains display diverse deformation-induced microstructures, i.e., kinked low-angle (0.5 to 5°) boundaries within Py1, curvilinear low-angle boundaries penetrating both Py1 and Py2, and foam-like textured Py3. These microstructures may offer pathways to transport exotic fluids, leading to superimposed microstructures in early-formed pyrite. Integrated μ-XRF, EMPA, APT, and HRTEM data sets present grain- to nanometer-scale elemental distributions of Au, As, Bi, and Te, and reveal that the Bi-(Te)-rich mineral associations, rather than arsenian pyrite, are major gold carriers in the polymetallic sulfide veinlet. The superimposed microstructures in pyrite reveal that the major Au mineralization stage likely comprises two episodes of ore-forming fluids. The early-episode fluids had T-fO2 condition overlapping the stable field of pyrrhotite, which dissolved Py1 and developed Bi-(Te)-rich melts as major Au scavengers. The late-episode fluids crystallized arsenian Py2 containing 20–60 ppm of invisible gold. This study highlights the effectiveness of multiple techniques to reveal complex microstructures of pyrite, which can serve as critical fingerprints to establish a temporal framework of fluid evolution and Au deposition in lode gold deposits.
  PubDate: 2022-06-01
The formation of (Ni-Co-Sb)-Ag-As ore shoots in hydrothermal
galena-sphalerite-fluorite veins
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  Abstract: Abstract Unusual hydrothermal native As-sulfide ± native Ag ± arsenide ± antimonide ± sulfosalt ore shoots and their co-genetic sulfide-fluorite-barite-quartz host veins, which are common in the region and in whole Central Europe, were investigated at three localities in the Schwarzwald, SW Germany, to understand the physico-chemical processes governing the change from a normal (= common) hydrothermal to an exceptional ore shoot regime. Based on fluid inclusions, the formation of the gangue minerals is the result of binary mixing between a NaCl-rich brine and a CaCl2-rich brine (both ~ 20 wt% NaCl aq.). This mixing correlation, major and minor fluid composition, formation temperature (~ 150 °C), and δ34S signature are identical (within error) in ore shoots and host veins. Thermodynamic modeling indicates that ore shoot formation must have resulted from a change in redox conditions by a local influx of a volumetrically minor reducing agent, probably hydrocarbons. The elemental content and the mineralogy of each ore shoot locality (Ag-As-rich: Münstertal; Ag–Ni-As-rich: Urberg; Ag–Ni-As-Sb-rich: Wieden) reflect the metal content of the binary mixed fluid, while mineral textures, successions, and assemblages are thermodynamically and, regarding sulfur, kinetically controlled. The formation of vein and ore shoot sulfides requires an addition of sulfide, most probably from the sulfide-bearing host rocks, because thermodynamic and kinetic reasons suggest that the two major vein-forming and metal-bearing fluids are not the source of the sulfur. The final ore shoot textures are influenced by later hydrothermal remobilization processes of As and Ag. This results in a number of sulfosalts, mostly proustite-pyrargyrite. Interestingly, the greater thermodynamic stability of Sb-endmember sulfosalts enables them to form even in As-dominated fluid systems.
  PubDate: 2022-06-01
A geochemical study of the Sweet Home mine, Colorado Mineral Belt, USA:
formation of deep hydrothermal vein–type molybdenum greisen and base
metal mineralization
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  Abstract: Abstract Deep hydrothermal Mo, W, and base metal mineralization at the Sweet Home mine (Detroit City portal) formed in response to magmatic activity during the Oligocene. Microthermometric data of fluid inclusions trapped in greisen quartz and fluorite suggest that the early-stage mineralization at the Sweet Home mine precipitated from low- to medium-salinity (1.5–11.5 wt% equiv. NaCl), CO2-bearing fluids at temperatures between 360 and 415 °C and at depths of at least 3.5 km. Stable isotope and noble gas isotope data indicate that greisen formation and base metal mineralization at the Sweet Home mine was related to fluids of different origins. Early magmatic fluids were the principal source for mantle-derived volatiles (CO2, H2S/SO2, noble gases), which subsequently mixed with significant amounts of heated meteoric water. Mixing of magmatic fluids with meteoric water is constrained by δ2Hw–δ18Ow relationships of fluid inclusions. The deep hydrothermal mineralization at the Sweet Home mine shows features similar to deep hydrothermal vein mineralization at Climax-type Mo deposits or on their periphery. This suggests that fluid migration and the deposition of ore and gangue minerals in the Sweet Home mine was triggered by a deep-seated magmatic intrusion. The findings of this study are in good agreement with the results of previous fluid inclusion studies of the mineralization of the Sweet Home mine and from Climax-type Mo porphyry deposits in the Colorado Mineral Belt.
  PubDate: 2022-06-01
The Schlaining quartz-stibnite deposit, Eastern Alps, Austria: constraints
from conventional and infrared microthermometry and isotope and
crush-leach analyses of fluid inclusions
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  Abstract: Abstract Stibnite was mined until the end of the twentieth century in the Schlaining ore district, Austria, near the easternmost border of the Eastern Alps where windows of Penninic ophiolites and metasediments are exposed below Austroalpine tectonic units. In Early Miocene, structurally controlled small vein and metasomatic stibnite-quartz deposits were formed in Penninic Mesozoic calcareous marbles and calcite schists. Fluid inclusion studies identified two fluids involved in the mineralization: (i) a low-salinity, low-CO2 metamorphic fluid that precipitated quartz at approximately 240 °C and (ii) a stibnite-forming ore fluid that had a meteoric origin. There is no evidence of boiling or that the fluids mixed during mineralization. The ore components Sb and H2S were leached by fluid/rock interaction from buried rock units. Stibnite mineralization occurred by cooling the ore fluid to below 300 °C, at less than 2000 m depth. Quartz precipitated at slightly lower temperatures, approximately contemporaneous with stibnite. Fluid migration and ore deposition are probably related to high heat flow during the exhumation of the Rechnitz Window in response to Neogene extension and/or shallow Early Miocene andesitic magmatism. The study emphasizes that data obtained from the analyses of gangue minerals alone cannot routinely be used to infer the origin and depositional conditions of the associated ore minerals.
  PubDate: 2022-06-01
Gold refinement by the fractionation of Bi-enriched partial melts at the
Quadrilátero Ferrífero, Brazil: implications on the formation of
hypozonal deposits
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  Abstract: Abstract Several gold deposits display complex Bi-bearing mineralogy. Bismuth-bearing phases are generally sensitive to changes in physicochemical conditions such that the interpretation of Bi–Au associations is useful to understand these mineralizing systems. However, gaps in the physicochemical constraints given by the Bi enrichment in these systems prevent robust metallogenic models in some complex deposits. São Sebastião is a hypozonal gold deposit in the Quadrilátero Ferrífero historic mining district in Brazil, and unlike other Archean gold deposits in this area, it displays a disseminated high-temperature and high-grade sulfide overprint with Bi enrichment. The Bi-bearing mineralogy at São Sebastião is heterogeneously distributed in the BIF-hosted ore bodies. Bismuth-sulfosalts, Bi-chalcogenides, and native bismuth have crystallized in a variable set of intercalated patches, yielding different ore facies given by the fractionation of hydrothermally assisted melts. Base metal–bearing Bi-sulfosalts, electrum, and acanthite result from high-temperature (~ 600 °C) immiscible melts rich in chloride ligands, while late crystallization of high-fineness native gold associated with native bismuth at 271 °C is evidence for Au scavenging by protracted low-temperature Bi-enriched metallic melts. This mechanism has favored gold remobilization from early sulfide assemblages and the development of localized upgraded ore stringers. Rapid uplift from a reduced (low fO2) hypozonal environment to oxidized brittle conditions is suggested by crosscutting bismuthinite-bearing veins’ fluid inclusion patterns and the absence of maldonite (Au–Bi alloy). Many hypozonal deposits like São Sebastião show similar mineralogy and have developed at the boundaries of Archean terrains, registering multiple tectonic overprints where partial melts may have had an essential role in the final ore formation.
  PubDate: 2022-06-01
Karst-hosted Mississippi Valley-type Pb–Zn mineralization in fold-thrust
systems: a case study of the Changdong deposit in the Sanjiang Belt, China
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  Abstract: Abstract Karst is the most common ore-controlling structure in Mississippi Valley-type (MVT) Pb–Zn deposits. However, the formation process of karst caves that contain ores and their related Pb–Zn mineralization in fold-thrust belts is poorly understood. The Changdong MVT Pb–Zn deposit is hosted by karst caves located in the fold-thrust system of the Simao basin, Sanjiang metallogenic belt, Tibetan Plateau. The Changdong deposit is an ideal natural laboratory for studying the effects of karst on Pb–Zn mineralization in MVT deposits. The ore bodies in this deposit are hosted by a large-scale carbonate breccia and bedded sediments belt within the late Permian limestones, which are situated in the hanging wall of the regional Longshu thrust fault. The δ13CV-PDB values of the limestone fragments from the breccias range from − 4.2 to 4.1‰. They are similar to those of overlying limestone strata, indicating that the fragments were mainly derived from autochthonous limestones in the overlying strata. Energy-dispersive spectroscopy analysis indicates that the bedded sediments and the matrices of the carbonate breccias contain K–Al silicate clay minerals, quartz, rock fragments, and calcite fragments. Detrital zircons from bedded sediments contain five discrete age populations ranging from the Jurassic to the Paleoproterozoic, indicating that the matrix materials were derived from the weathered sediments of metamorphic and magmatic rocks along the western margin of the Simao basin. Bedded sediments dominated by exogenous materials are actually speleothems. When contextualized with recently published data placing the Changdong deposit formation in the early to middle Oligocene, our data suggest that the Changdong deposit formed within a meteoric paleokarst system. The Pb–Zn ores are hosted by the speleothems in the breccia belt and comprise microspherulitic or colloidal sphalerite and euhedral galena. The sphalerite and galena precipitated by filling voids and replacing calcite crystals in faded speleothems. The pyrite and galena δ34SV-CDT values from the Changdong deposit range from − 16.9 to 15.8‰, indicating a pre-existing H2S reservoir interpreted as a result of bacterial sulfate reduction (BSR). A three-stage process for the Changdong deposit was proposed as last. First, the Permian limestone was uplifted to the near-surface by regional thrusting during the India-Eurasia collision, and karst caves formed by meteoric dissolution. Second, a reduced sulfur trap formed by BSR in the paleokarst caves during continual regional compression. Third, metal-rich fluids migrated into the Changdong deposit via tensile faults formed during the transition from compressive stress to extensional strike-slip stress as a result of progressive rotation of the regional strain axes. The Pb–Zn sulfides were likely precipitated by low-temperature fluid mixing. This study provides new data to establish a geologically consistent framework for the evaluation of karst caves and related MVT Pb–Zn mineralization in fold-thrust systems.
  PubDate: 2022-06-01
190Pt-4He dating of platinum mineralization in Ural-Alaskan-type complexes
in the Kamchatka region: evidence for remobilization of platinum-group
elements
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  Abstract: Abstract Ural-Alaskan-type zonal mafic–ultramafic complexes are the predominant source of platinum-group minerals (PGM) in alluvial deposits worldwide. Processes responsible for the formation of mm-sized grains of Pt-Fe alloys within these deposits remain a subject of ongoing debate. In this study, the 190Pt-4He dating method is applied to isoferroplatinum from the Ural-Alaskan-type Matysken, Itchayvayam, and Filippa complexes of the Koryak-Kamchatka Platinum Belt in order to determine the timing of Pt mineralization and its relation to the regional and local geologic history of the source rocks. Results of 190Pt-4He dating indicate multistage Pt mineralization, with at least two generations recognized. The first generation (70 ± 2 Ma and 77 ± 2 Ma for the northern and southern parts of the Belt, respectively) is contemporaneous with intra-oceanic arc magmatism, which resulted in the formation of the dunite-clinopyroxenite complexes. The second generation is significantly younger (~ 64 Ma), and reflects a later mineralization or recrystallization event following the termination of active volcanism within the Olyutorsky Arc evolution.
  PubDate: 2022-06-01
Archetypal Au-bearing silica sinter from the Miocene Milestone deposit,
Idaho, USA
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  Abstract: Abstract The Milestone silica sinter defines a mid-Miocene epithermal paleosurface that is adjacent to the DeLamar Ag–Au deposit in the Silver City District (SCD), Idaho. Milestone, DeLamar, and other SCD deposits (e.g., War Eagle and Florida mountain) are part of the same suite of ~ 17–14 Ma bonanza Au–Ag deposits associated with volcanism that demarcates the onset of the Yellowstone hotspot across the northern Great Basin (USA). Geologic mapping of the Main Knob of Milestone reveals five lithofacies in the paleosurface: matrix-supported breccia, clast-supported breccia (cross-cut by near-vent silica gel), silica sinter and geyserite, and bioformations. The facies are indicative of a paleohot spring, typical of active hot spring environments. Electrum microparticles occur in dark-gray to black bands in the sinter, which resemble high-grade ore-bearing ginguro bands in epithermal veins. Transect and spot trace element analyses by LA-ICP-MS show that these sinter bands are associated with metal(loid) concentrations (0.03–291 ppm Au and 0.19–28,400 ppm Ag). The metal-rich bands show textures that reflect the transportation and deposition of Au-rich particles. These textures, coupled with a lack of compositional variation across the different sinter facies (distance from hot springs vent), suggest that the Au-rich particles formed at depth and were then transported to the surface. This occurrence of precious metals in Milestone sinter likely indicates metal-bearing veins at depth, along faults and other structural weaknesses that channeled the liquid to the surface. Milestone sinter, first recognized by Lindgren, is analogous to those of the Yellowstone and Taupo Volcanic Zone geothermal systems.
  PubDate: 2022-05-20
Detrital zircon ages from Archaean conglomerates in the Singhbhum Craton,
eastern India: implications on economic Au-U potential
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  Abstract: Abstract New U–Pb age and Hf isotope data obtained on detrital zircon grains from Au- and U-bearing Archaean quartz-pebble conglomerates in the Singhbhum Craton, eastern India, specifically the Upper Iron Ore Group in the Badampahar Greenstone Belt and the Phuljhari Formation below the Dhanjori Group provide insights into the zircon provenance and maximum age of sediment deposition. The most concordant, least disturbed 207Pb/206Pb ages cover the entire range of known magmatic and higher grade metamorphic events in the craton from 3.48 to 3.06 Ga and show a broad maximum between 3.38 and 3.18 Ga. This overlap is also mimicked by Lu–Hf isotope analyses, which returned a wide range in εHf(t) values from + 6 to − 5, in agreement with the range known from zircon grains in igneous and metamorphic rocks in the Singhbhum Craton. A smaller but distinct age peak centred at 3.06 Ga corresponds to the age of the last major magmatic intrusive event, the emplacement of the Mayurbhanj Granite and associated gabbro, picrite and anorthosite. Thus, these intrusive rocks must form a basement rather than being intrusive into the studied conglomerates as previously interpreted. The corresponding detrital zircon grains all have a subchondritic Hf isotopic composition. The youngest reliable zircon ages of 3.03 Ga in the case of the basal Upper Iron Ore Group in the east of the craton and 3.00 Ga for the Phuljhari Formation set an upper limit on the age of conglomerate sedimentation. Previously published detrital zircon age data from similarly Au-bearing conglomerates in the Mahagiri Quartzite in the Upper Iron Ore Group in the south of the craton gave a somewhat younger maximum age of sedimentation of 2.91 Ga. There, the lower limit on sedimentation is given by an intrusive relationship with a c. 2.8 Ga granite. The time window thus defined for conglomerate deposition on the Singhbhum Craton is almost identical to the age span established for the, in places, Au- and U-rich conglomerates in the Kaapvaal Craton of South Africa: the 2.98–2.78 Ga Dominion Group and Witwatersrand Supergroup in South Africa. Since the recognition of first major concentration of gold on Earth’s surface by microbial activity having taken place at around 2.9 Ga, independent of the nature of the hinterland, the above similarity in age substantially increases the potential for discovering Witwatersrand-type gold and/or uranium deposits on the Singhbhum Craton. Further age constraints are needed there, however, to distinguish between supposedly less fertile (with respect to Au) > 2.9 Ga and more fertile < 2.9 Ga successions.
  PubDate: 2022-05-17
Porphyry-epithermal Cu-Mo-Au–Ag mineralization in the Nakhodka ore
field, Baimka Trend, Chukotka, Russia: a geological, mineralogical, and
geochemical perspective
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  Abstract: Abstract The Nakhodka ore field (NOF) is situated in the Baimka Trend, Chukotka, Russia, and comprises the Vesenny epithermal Au–Ag, and Malysh, Nakhodka, Vesenny III, and Pryamoy porphyry Cu-Au ± Mo deposits. Porphyry and epithermal mineralization of the NOF are hosted by Early Cretaceous diorite and monzonite intrusions, which are dated at 139–141 Ma (U–Pb zircon). The NOF mineralization is structurally controlled. The prevailing stress field during the evolution in the Baimka dextral shear zone (also known as Baimka Trend) has led to the formation of extensional and strike-slip structures that control distinct zones with strong quartz-sericite alteration and sheeted high-grade quartz–sulfide veining; characteristics that are similar to the world-class Peschanka porphyry Cu-Au deposit located about 20 km to the NW of the NOF. Four types of hydrothermal alteration are documented in the NOF: (1) potassic, (2) propylitic, (3) quartz-sericite, and more rarely (4) argillic. Two phases of porphyry-style mineralization are distinguished: (1) early-stage quartz-magnetite veining associated with potassic alteration and (2) sheeted quartz-sulfide (bornite, chalcopyrite, molybdenite, pyrite) veining that is spatially associated with a strong quartz-sericite alteration assemblage. Epithermal Au–Ag mineralization belongs to the intermediate-sulfidation type and consists of gold-bearing polymetallic quartz-dolomite ± rhodochrosite veins and veinlets. The NOF is defined by a distinct geochemical zonation. Geophysical data show that the high-grade stockwork zones at the Vesenny III porphyry Cu-Au deposit are defined by pronounced magnetic anomalies reflecting abundant hydrothermal magnetite veining, while the Vesenny epithermal Au–Ag deposit is defined by a strong negative magnetic anomaly due to strong silicification and magnetite-destructive quartz-sericite to argillic alteration.
  PubDate: 2022-05-17
Scheelite chemistry from skarn systems: implications for ore-forming
processes and mineral exploration
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  Abstract: Abstract The trace element composition of scheelite from 19 well-documented reduced and oxidized skarn systems was measured by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to establish chemical criteria for the application of scheelite as an efficient indicator mineral for mineral exploration targeting. In both reduced and oxidized skarns systems, scheelite forms during prograde and retrograde stages. Prograde scheelite is texturally and chemically zoned, whereas retrograde scheelite is predominantly texturally homogeneous but may display chemical zonation. Five chondrite-normalized REE patterns, displaying both positive and negative Eu anomalies, are identified in the data: (i) steep and (ii) shallow negative slopes, (iii) concave, (iv) flat to slightly concave, and (v) convex shapes. The different REE patterns are related to variable fluid salinity and association with co-precipitated garnet or clinopyroxene. Results of partial least square-discriminate analysis (PLS-DA) show that scheelite composition varies according to skarn redox, intrusion composition, and metal association. These results support the fact that the trace element composition of scheelite is in part a function of igneous rock composition and oxygen fugacity, in addition to salinity, co-genetic minerals, and composition of the mineralizing fluids. Scheelite from reduced and oxidized skarns can be discriminated from those from orogenic and intrusion-related gold deposits due to their lower Sr and higher Mo, Ta, and Nb concentrations. Scheelite trace element composition investigated by PLS-DA is effective in discriminating different deposit types, supporting the use of scheelite as an indicator mineral for exploration targeting.
  PubDate: 2022-05-10
Genesis of the Maogongdong deposit in the Dahutang W-Cu-(Mo) ore field of
northern Jiangxi Province, South China: constraints from mineralogy, fluid
inclusions, and H-O-C-S isotopes
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  Abstract: Abstract The Maogongdong deposit is located in the giant Dahutang W-Cu-(Mo) ore field, northern Jiangxi Province, South China. It is mainly a vein-type deposit, characterized by early W and late Cu-Mo mineralization, and temporally and spatially associated with Late Mesozoic S-type muscovite granites emplaced into a Neoproterozoic granodiorite batholith and the Shuangqiaoshan Group metasedimentary rocks. Fluid inclusions and H–O isotopes suggest that the early ore-forming fluids of the Maogongdong deposit are mainly magmatic water with relatively high temperature (270–410 °C) and moderate-to-low salinity, while the late ore-forming fluids are mixed with meteoric water, with medium-to-low temperature (160–270 °C) and low salinity. Infrared and conventional microthermometric studies of fluid inclusions of the main tungsten mineralization stage show that the homogenization temperatures of primary fluid inclusion assemblages in wolframite (325 to 355 °C) are about 20 °C higher than those of coexisting scheelite and generally 40 °C higher than those in quartz. The δ34S values of sulfides (− 5.2 to − 1.3 ‰) in the sulfide stage are slightly lower than the magmatic sulfur (− 1.7 to 0.6 ‰) in the pre-ore stage, most likely due to an increase in oxygen fugacity. The low carbon isotope values (− 26.2 to − 15.5 ‰) of fluid inclusions in the tungsten mineralization stage show that a large amount of organic carbon was added before mineralization. Fluid cooling and pressure decrease are the main factors of tungsten ore precipitation, while local boiling may also make a contribution. Mixing of the different fluids led to the formation of copper and molybdenum ores.
  PubDate: 2022-04-29
Formation, remobilisation and alteration processes at inactive
hydrothermal vents: insights from elemental analysis of Cu-(Fe-)S sulfides
from TAG, Mid-Atlantic Ridge
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  Abstract: Abstract Chalcopyrite is the main Cu mineral in mafic-hosted marine hydrothermal systems. Its trace element budget and that of its alteration products may hold valuable information on formation, remobilisation and alteration processes of the hydrothermal system. In this study, we analysed chalcopyrite from five inactive seafloor massive sulfide (SMS) sites from the TAG hydrothermal field on the Mid-Atlantic Ridge by electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for 24 elements. Twelve of them are discussed in detail. In general, trace element concentrations range between sub-parts per million (ppm) to several hundreds of ppm. The elements Se and Co are incorporated into the lattice at high temperatures of > 300 °C, whereas As, Ge, Ga substitute into the structure at intermediate to low temperatures. Other elements, e.g. Zn, are either accommodated into the mineral lattice or form inclusions, whereas V and Mn, which originate from seawater, get adsorbed onto the mineral surface. Idaite, chalcocite, and covellite exhibit similar trace element patterns to those of the precursor chalcopyrite. However, the secondary copper minerals show enrichment of Ag and Mo. Factors controlling the incorporation are predominantly related to changes in physicochemical conditions with the host rock composition playing only a minor role.
  PubDate: 2022-04-27
New insights about the origin of the Shilu Fe-Cu-Co deposit, Hainan
Island, South China, with emphasis on the regional metallogeny
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  Abstract: Abstract The giant Shilu Fe-Cu-Co deposit in Hainan Island, South China, which was structurally and hydrothermally superimposed, is mainly hosted in highly metasomatized dolostones/marbles of the ~ 900 Ma Shilu Group. This study confirmed that the ore bodies are originally strata-bound and epigenetic, but do not have spatial relations with any coeval intrusions. In this study, the paragenetic sequence of the pre-deformation mineralization is refined and consists of early Ca-silicate alteration (I), Fe (II), and Cu-Co (III) mineralization stages, followed by multiple overprints and/or undeformed veins (stage IV). Our new oxygen and in situ Pb–S isotopic results for stages I to III show that the mineralizing fluids were initially magmatic-hydrothermal but have undergone variable degrees of interaction with country rocks during mineralization. On the other hand, stage IV fluids have in situ Pb–S isotopic compositions indicative of significant contributions of early-stage components through secondary re-mobilization. These features, in combination with chemical compositions of Fe oxides (e.g., elevated Ti in hematite), strongly argue that the Shilu deposit does not belong to BIF as previously considered, but is typical of magmatic-hydrothermal IOCG deposits. New sulfide Re-Os isotopic data show that the major Fe-Cu-Co mineralization formed at 780 ± 24 Ma (MSWD = 0.62). The deposit is confirmed to be broadly comparable to Neoproterozoic IOCG deposits in the Ailao Shan-Red River shear zone in terms of timing and nature of mineralization. Given that the shear zone likely extends to Hainan Island, the Shilu deposit is considered to be part of the same IOCG metallogenic belt and similar mineralization along the shear zone may be more widespread than previously thought.
  PubDate: 2022-04-25
Timing and sources of skarn mineralization in the Canadian Tungsten Belt:
revisiting the paragenesis, crystal chemistry and geochronology of apatite
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  Abstract: Abstract Five generations of fluorapatite in mineralized skarn and host rocks from the Mactung W (Cu-Au) deposit, Northwest Territories, Canada, are identified based on petrographic, compositional and geochronological (U–Pb) data. These data, coupled with new (in this study) and previously published data on apatite from the nearby Cantung deposit, provide constraints on the timing of skarn mineralization, as well as metal and fluid sources of the Canadian Tungsten Belt. Type-i apatite of the Mactung deposit formed from ~ 106 ± 4 to 103 ± 2 Ma through recrystallization of sedimentary apatite (type-o apatite) during regional metamorphism, pre-skarnification. Type-i apatite is W-rich (up to 47.6 ppm) and occurs with coeval scheelite and titanite, indicating a potential sedimentary source, perhaps from detrital rutile, for W. Apatite crystals in prograde (type-ii) and retrograde (type-iii and type-iv) skarns yield ages from ~ 96 ± 1 to 92 ± 1 Ma, overlapping with Mactung biotite-granite plutons and late-stage felsic dykes and confirming skarn formation during emplacement of the granites over a period of ~ 5 million years. Type-ii apatite contains high rare earth element that increases with increasingly negative Eu anomalies, suggesting prograde fluids were sourced from a felsic melt undergoing fractional crystallization. Retrograde apatite exhibits weak lanthanide tetrad effects with superchondritic Y/Ho ratios (> 38), suggesting retrograde fluids exsolved from a highly evolved magmatic source. Apatite crystals from the Cantung skarn deposit are compositionally and paragenetically similar to those from the Mactung apatite and yield ages similar to the Cantung biotite-monzogranite plutons and late-stage felsic dykes. We conclude prograde fluids were derived from biotite-granites, whereas retrograde fluids exsolved from evolved melts recorded by later felsic dykes.
  PubDate: 2022-04-25
Trace element distribution and geochemical zonation in the world-class
Nowa Sól sediment-hosted Cu-Ag deposit, SW Poland
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  Abstract: Abstract More than 200 samples from sediment-hosted Lower Zechstein Cu-Ag series of the newly discovered Nowa Sól deposit (SW Poland) were studied in order to determine spatial and vertical correlations between the metals. On the basis of obtained metal distribution, the investigated deposit can be subdivided into two parts. Rare earth elements and gold concentrations are elevated in the southwestern part of the deposit, close to the Rote Fäule area. Silver cobalt, rhenium, lead, and zinc are concentrated in a wide polymetallic zone in the northeastern part of the deposit. The concentration patterns of most metals are controlled by the distance from the Zielona Góra oxidized field. Copper content does not vary significantly across the deposit. The contents of molybdenum, nickel, and vanadium seem to depend on the lithotype rather than on broader metal distribution. In general, the highest ore grades are observed in the organic-rich variety of the Kupferschiefer, in the uppermost mineralized Weissliegend, and in the base of the Zechstein limestone. Metal zonation of the Nowa Sól deposit can be drawn in the following order from southwest to northeast: (1) Au-rare earth element (REE)-bearing transitional zone, (2) REE-enriched Cu-bearing reduced zone, (3) Ag-Re-Co-enriched Cu-bearing reduced zone, (4) Pb-Ag-Co-enriched Cu-bearing reduced zone, and (5) Pb-bearing reduced zone. Distribution of metals across the investigated area supports an epigenetic model involving multistage and fault-controlled ore-forming processes. It is plausible that the volume, temperature, chemical composition, and time of activity of the metalliferous fluids have differed across the northern part of the Fore-Sudetic Monocline. The polymetallic Nowa Sól deposit, hosting estimated, inferred, and indicated resources of 10.6 Mt of Cu and 36.4 kt of Ag, is part of a broader mineralized trend. The deposit is open towards the west and northwest; the prognostic area with hypothetical resources, covering more than 500 km2 has been delineated in the northwestern part of the Fore-Sudetic Monocline, where at least 50 Mt of Cu and 120 kt of Ag can still be discovered and documented.
  PubDate: 2022-04-21
Texture and geochemistry of pyrite from the Jinya, Nakuang and Gaolong
gold deposits in the Youjiang Basin: implications for basin-scale gold
mineralization
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  Abstract: Abstract To understand the controls of basin paleogeographic evolution on sediment-hosted gold metallogenesis, a study was undertaken of pyrite texture and geochemistry of the Jinya, Nakuang, and Gaolong gold deposits in the Youjiang Basin, SW China. Syn-sedimentary/diagenetic pyrite and three generations of hydrothermal pyrite (As-Au-poor core, anomalously As-rich but Au-poor mantle, and As-Au-rich rim) are defined in the three gold deposits. The syn-sedimentary/diagenetic pyrites deposited in the basin facies at Jinya and slope facies around platforms at Gaolong have δ34S values of –3.4 ‰ to + 7.3 ‰ and + 14.8 ‰ to + 16.1 ‰, respectively. Compared to As-Au-poor pyrite with abundant fine-grained galena inclusions and high-radiogenic Pb isotopic ratios, the As-Au-rich pyrite shows a ~ 2–3 ‰ increase in average δ34S values (Jinya: –5.9 ‰; Nakuang: –7.6 ‰; Gaolong: + 12.2 ‰) towards those of syn-sedimentary/diagenetic pyrite and a decrease in average Pb isotopic ratios. These phenomena can be explained by the interaction of ore fluids with the pyritic sedimentary host rocks. A regional feature of the Youjiang Basin is that most of the gold deposits share similar pyrite textures and trace element compositions. However, the δ34S values of auriferous pyrite range from –9 ‰ to –5 ‰, –5 ‰ to + 5 ‰, and + 5 ‰ to + 19 ‰ in these gold deposits with host rocks deposited in the basin facies, open platforms, and slope facies around platforms, respectively. Thus, it is demonstrated that the sulfur isotope compositions of auriferous pyrite were mostly determined by the syn-sedimentary/diagenetic pyrite formed under different sedimentary facies.
  PubDate: 2022-04-20
Correction to: Proceedings of the Ninth International Conference on
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  PubDate: 2022-04-07
Constraints on ore-forming fluid evolution and guidance for ore
exploration in the Zhaxikang Sb–Pb–Zn–Ag deposit in southern Tibet:
insights from silver isotope fractionation of galena
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  Abstract: Abstract This study reports the high-precision silver (Ag) isotopic compositions of the dominant Ag-bearing mineral (galena) in the representative Zhaxikang polymetallic deposit, which experienced a complex ore-forming process that can be divided into two episodes composed of six stages (first episode: Pb–Zn mineralization, stages 1 and 2; second episode: Sb mineralization, stages 3 to 6). The objective of this case study is to investigate the Ag isotopic fractionation mechanisms in a hydrothermal ore-forming system and explore the potential application of Ag isotopes. The earlier-generated stage 2 galena (0.17–6.07‰) has higher δ109AgNIST 978 Ag values with a significantly broader range in comparison to the subsequent stage 3 galena (–3.65 to 2.27‰). The δ109AgNIST 978 Ag values of galena also decrease from deep to shallow along with the trend of orebody V. These temporally and spatially decreasing trends indicate that the second episode of ore-forming fluid overprinted the first episode of mineralization along with the trend of orebodies from deep to shallow within the Zhaxikang orefield. A simple triple-phase separation model captures the temporal and spatial patterning of the data resulting from Ag isotopic fractionation, which is most likely related to the solid–liquid-vapor dynamics of the ore-forming fluid. According to approximate theoretical calculations, there is still great prospecting potential for Ag at depth within the Zhaxikang orefield. In summary, the Ag isotopes have the potential to trace phase changes, monitor ore-forming fluid evolution, constrain ore formation processes, and provide insights into ore exploration.
  PubDate: 2022-04-02