Episodes Of Mineralization Research Articles

Integration of multiple sulfur isotopes with structural analysis unveils the evolution of ore fluids and source of sulfur at the Kanowna Belle Archean orogenic gold deposit, Yilgarn Craton, Western Australia

The Kanowna Belle deposit is a world-class Archean orogenic gold system that witnessed multiple fluid episodes over a protracted deformation history. The hydrothermal fluid circulation episodes at the Kanowna Belle deposit initiated with the precipitation of early gold-bearing carbonate-famatinite-pyrite-telluride-electrum veins (V1a). These early veins were subsequently folded during a NE-SW shortening event (D1bKB) that led to the development of sericite-chlorite-pyrite stringers (V1b) and foliation (S1KB) dated at c. 2658 ± 9 Ma (U-Pb, xenotime). D1bKB structures are overprinted by quartz-carbonate-sericite-pyrite-gold veins (V2) controlled by the reverse faulting formed as a result of N-S shortening during D2KB. A subsequent deformation event (D3aKB) is related to sinistral shearing produced under ENE-WSW shortening and associated with the development of the Troy lodes and deposition of quartz-pyrite-sericite-gold veins (V3a) dated at c. 2628 ± 9 Ma (U-Pb, xenotime). The application of multiple sulfur isotope analyses of sulfides related to the different mineralization events resolves the hydrothermal fluid isotopic evolution through time. Despite the ore mineralogy differences of the V1, V2, and V3 vein sets, their associated sulfides yield small positive ∆33S (+ 0.1 to + 0.4‰; n = 231) values with two outliers (∆33S = + 0.5‰ and + 0.6‰) across all lithology types. The constant value of MIF-S through the three temporally different gold mineralization episodes implies that sulfur was derived from a single homogenized source of sulfur distal from the deposition site, irrespective of the Au endowment. The consistent small positive ∆33S sulfur isotope signature may support that the Archean orogenic gold system sourced sulfur and possibly hydrothermal fluids from a mantle/magmatic dominated source that homogenized with crustal sulfur at depth prior to gold deposition.

Mesozoic Metallogenesis of Peru: A Reality Check on Geodynamic Models

Abstract The Andean Cordillera is generally regarded as the product of easterly subduction of oceanic lithosphere below South America since the Late Triassic, but recent syntheses have challenged this paradigm. In one model, W-dipping oceanic subduction pulls the continent west until it collides with a ribbon continent that now forms the coastal region and Western Cordillera of the Peruvian Andes. A second model involves westerly oceanic subduction until 120 to 100 Ma, without the involvement of a ribbon continent, to explain deep, subducted slabs revealed by mantle tomographic images. Both assume that “Andean-style” E-dipping subduction did not exist during the Jurassic and Early Cretaceous. Another model, also involving mantle tomography, assumes that a back-arc basin opened inboard of the trench between 145 and 100 Ma, displacing the E-dipping subduction zone offshore without changing its polarity. This article examines the implications of these hypotheses for southern Peruvian metallogenesis during the Mesozoic, when marginal basins opened and closed and were thrust eastward and then were intruded, between 110 and ~50 Ma, by a linear belt of multiple plutons known as the Coastal Batholith. The earliest mineralization in southern Peru is located on the coast and comprises major iron oxide and minor porphyry copper deposits emplaced between 180 and 110 Ma. This was followed by Cu-rich iron oxide copper-gold deposits and a large Zn-rich volcanogenic massive sulfide (VMS) deposit between 115 and 95 Ma, then minor porphyry Cu deposits at ~80 Ma. A second episode of localized VMS mineralization followed at 70 to 68 Ma, then a group of at least five giant porphyry Cu-Mo deposits in southernmost Peru formed between 62 and 53 Ma. The conventional model of Andean-style subduction, which explains many features of Mesozoic Andean metallogenesis in terms of changing plate vectors and velocities, is a poor fit with mantle tomographic anomalies that are thought to record the paleopositions of ancient trenches. A ribbon-continent model requires some plutons of the Coastal Batholith to have been separated from others by an ocean basin. West-dipping oceanic subduction does not account for Jurassic mineralization and magmatism in southern Peru. A model involving a back-arc basin that opened inboard of the existing trench, forcing E-dipping subduction to retreat offshore between 145 and 100 Ma, seems to best explain the metallogenic and tomographic data.

Gold mineralization in the northern margin of the North China Craton: Influence of alkaline magmatism and regional tectonic during Middle Paleozoic-Mesozoic

The northern margin of North China Craton (NNCC) has undergone multiple tectonic and magmatic episodes associated with numerous gold mineralization during Devonian to Cretaceous. The origin of gold mineralization is a subject of debate in the NNCC, but there is a consensus on a metamorphic-hydrothermal origin and a magmatic-hydrothermal origin. For this study, we focused on four gold districts including the Daqingshan, Zhangjiakou, West Liaoning, and Changbaishan from west to east. We specifically constrain the link between the Hadamengou, Dongping, Jinchanggouliang, Erdaogou and Haigou gold deposits and their magmatic episodes. The Dahuabei and Haigou granites, and Dongping syenite rocks have an alkaline affinity. In contrast, the Xitaizi-Jinchanggouliang and Xiaoxigou granites as well as the Duimiangou quartz monzonites are calc-alkaline with high alkaline rocks. They are predominantly metaluminous and high fractionated I-type granites, except the Xiaoxigou granite which is A-type granites with peraluminous nature. This indicates a variable mixing between depleted mantle-derived mafic magma and ancient crust derived magma.The magmatic events overlap the gold mineralization episodes in the NNCC. We have identified four magmatic episodes during Middle Paleozoic to Mesozoic at 400–320 Ma, 245–221 Ma, 199–161 Ma, and 143–125 Ma. On the other hand, gold mineralization was emplaced from Carboniferous to Cretaceous (390–110 Ma) with a peak in the Middle Jurassic (170–160 Ma).The available sulfur, oxygen, and carbon isotopic data from the studied NNCC gold deposits suggest that the ore-forming fluids were derived from a mixture of magmatic fluids and meteoric waters that flow in the wall rocks, except for the Hadamengou and Jinchanggouliang gold deposits. Both late deposits present a multi-source involving organic matter and other regional crustal rocks as shown by their positive δ34S values (0.6–18.5‰). The intrusive rocks and sulfides in the NNCC display similar lead isotope data, suggesting that the lead isotopes might have similar origin. The gold-forming materials resulting from the mixing of these fluids are the product of several alkaline magmatism activities in this region. Hence, this study has proved that gold mineralization is spatially and temporally related to the alkaline magmatism in the NNCC.The dominant tectonic events in the NNCC are marked by post-collisional or anorogenic geodynamical setting which is characterized by high alkaline features and Andean-type arc related to subduction geodynamical setting and characterized by calc-alkaline features of the studied rocks. Both tectonic events are controlled by: (1) the collision between the NCC and the Bainaimiao arc, (2) the subduction of the Paleo-Asian-ocean plate beneath the NCC, (3) the collision between the Siberian Craton and the NCC, and (4) the subduction of the western Paleo-Pacific beneath the NCC. These tectonic regimes are expressed by a transitional regime changing from compression to extension at western and an extensional regime at western and eastern parts of the NNCC, respectively.

Occurrence and Distribution of Silver in the World-Class Río Blanco Porphyry Cu-Mo Deposit, Central Chile

Abstract Porphyry Cu-Mo deposits (PCDs) are the world’s major source of Cu, Mo, and Re and are also a significant source of Au and Ag. Here we focus on the world-class Río Blanco PCD in the Andes of central Chile, where Ag is a by-product of Cu mining. Statistical examination of an extensive multielemental inductively coupled plasma-mass spectrometry data set indicates compositional trends at the deposit scale, including Ag-Cu (r = 0.71) and Ag-In (r = 0.53) positive correlations, which relate to Cu-Fe sulfides and Cu sulfosalts in the deposit. Silver is primarily concentrated in Cu ores in the central core of the deposit, and significant variations in the Ag concentration are related to the different hydrothermal alteration types. The concentration of Ag is highest in the potassic core (avg 2.01 ppm) and decreases slightly in the gray-green sericite (phyllic) zone (avg 1.72 ppm); Ag is lowest in the outer propylitic alteration zone (avg 0.59 ppm). Drill core samples from major hydrothermal alteration zones were selected for in situ analysis of Ag and associated elements in sulfide and sulfosalt minerals. To ensure representativeness, sample selection considered the spatial distribution of the alteration types and ore paragenesis. Chalcopyrite is the most abundant Cu sulfide in Río Blanco, with Ag concentration that ranges from sub-parts per million levels to hundreds of parts per million. The highest concentration of Ag in chalcopyrite is associated with the high-temperature potassic alteration stage. Bornite is less abundant than chalcopyrite but has the highest Ag concentration of all studied sulfides, ranging from hundreds of parts per million up to ~1,000 ppm. The Ag concentration in bornite is higher in lower-temperature alteration assemblages (moderate gray-green sericite), opposite to the behavior of Ag in chalcopyrite. Pyrite has the lowest Ag content, although concentrations of other critical elements such as Co, Ni, and Au may be significant. The highest Ag concentrations, i.e., thousands of parts per million up to weight percent levels, were detected in late-stage Cu sulfosalts (enargite, tennantite, and tetrahedrite). The Ag content in these sulfosalts increases with increasing Sb concentrations, from the Sb-poor enargite to the Sb-rich tetrahedrite. The earliest Ag mineralization event is related to the potassic alteration stage represented by early biotite and transitional early biotite-type veinlets and where the predominant sulfides are chalcopyrite and bornite. Silver mineralization during this stage was predominantly controlled by crystallization of Cu-Fe sulfides. The second Ag mineralization event at Río Blanco is associated with the transitional Cu mineralization stage, which is represented by the gray-green sericite alteration (C-type veinlets). In this alteration type, Ag was partitioned preferentially into chalcopyrite, bornite, and to a lesser extent pyrite. The last Ag mineralization event is related to the late quartz-sericite alteration stage, characterized by D- and E-type veinlets with pyrite-chalcopyrite and enargite-tennantite-tetrahedrite. Our data indicate that Ag was associated with several Cu mineralization episodes at Río Blanco, with Ag concentration apparently controlled by cooling, changes in pH, fO2 and fS2 of the hydrothermal fluids, and the intensity of alteration. Overall, our results provide information on critical metal partitioning between sulfides, plus the distribution of critical element resources at the deposit scale. Knowledge of the mineralogical occurrence of critical metals in PCDs is necessary to better assess their resources and evaluate the potential for their recovery.

Early Miocene metallogenic event formed the Bosawa low‐sulfidation epithermal gold deposit, Northeast Japan arc

AbstractThere are a number of epithermal Au‐Ag deposits in the Tohoku region of the Northeast Japan arc; however, these deposits have undergone limited exploration for over the past seven decades. This reconnaissance research study of the Bosawa deposit in Akita Prefecture was conducted to support future gold exploration in the Tohoku region. The Bosawa deposit is a vein‐type Au‐Ag deposit, with a production of 42,486 t of ore at 7.01 g/t Au and 14.9 g/t Ag recorded for the period from 1936 to 1957; mining started in the 18th century. The deposit consists of the Ohgiri vein system, which is hosted in felsic volcanic rocks of the Early Miocene Katsurabuchi Formation. The study included geological prospecting, ore description, K‐Ar dating, and fire assay analyses. The deposit is characterized by (a) strongly silicified host lapilli tuff fringed by pyrite‐adularia‐illite alteration; (b) presence of sulfide‐poor banded quartz veins with adularia; (c) abundance of bladed quartz in veins, pseudomorphs after bladed calcite; (d) presence of colloform opal texture in veins; and (e) simple ore mineralogy consisting of gold and argentite. These characteristics are typical of low‐sulfidation epithermal Au deposits. The K‐Ar age of adularia (19.33 ± 0.45 Ma) indicates that mineralization at Bosawa is distinctly older than the ages of other epithermal deposits in the Tohoku region but similar to the age of the initial mineralization episode of the Sado and Tsurushi deposits (24.4–22.1 Ma), Japan's second largest gold producer. This mineralization age coincides with the start of rifting of the Northeast Japan arc and separation from the Asian continent. As the felsic rocks related to this rifting event are widespread in the arc, and some are associated with epithermal gold deposits, the confirmation of typical low‐sulfidation style of mineralization in the Early Miocene provides evidence for a previously unrecognized metallogenic event in the Tohoku region.

Multiple rejuvenation episodes of a silicic magma reservoir at the origin of the large diatreme-dome complex and porphyry-type mineralization events at Cerro de Pasco (Peru)

The Cerro de Pasco district in central Peru hosts one of the world largest porphyry-related epithermal polymetallic deposits. The district is centered onto a large diatreme-dome complex crosscut by numerous dacite to rhyodacite bodies showing domal structures and quartz-monzonite dykes. Three temporally distinct high-temperature porphyry-type mineralization events have been recognized (PM1, PM2, and PM3). Dating of the latter by molybdenite Re-Os and by zircon U-Pb (LA-ICP-MS and CA-ID-TIMS) geochronology complements the already available dataset of zircon U-Pb ages of the subvolcanic and volcanic rocks mostly dacitic in composition occurring in the district and shows the existence of successive short-lived episodes (<100 kyr) of shallow magmatic activity and porphyry-type mineralization. The new geochronology data indicate that the magmatic system was active during more than 400 kyr, spanning from 15.59 ± 0.12 Ma to 15.16 ± 0.04 Ma, punctuated by three porphyry-type mineralization events that are precursors (maximum gap of 0.9 Myr) of the last stage of epithermal polymetallic mineralization at Cerro de Pasco. Detailed petrographic and geochemical (whole rock and minerals) studies have been performed and silicate melt inclusions hosted in quartz phenocrysts from the subvolcanic and volcanic rocks emplaced between and after the different porphyry-type mineralization events have been analyzed by LA-ICP-MS. Our results suggest that prior to their emplacement at shallow level, magmas were stored at depth with a high degree of crystallinity (>50%) at pressures between 0.9 and 3.4 kbar and at temperatures between ~680 °C and ~725 °C. At such conditions, magma is beyond the point of rheological lock-up and is not eruptible. The emplacement of the mostly dacitic subvolcanic and volcanic rocks has required a series of rejuvenation events of the upper crustal high-crystallinity silicic magma reservoir. Field relationships and geochronology indicate that emplacement of the subvolcanic and volcanic rocks is preceded each time by high-temperature (>600 °C) quartz-pyrite-magnetite ± chalcopyrite and quartz-molybdenite veining forming the three recognized porphyry-type mineralization events. Hydrothermal quartz of these veins host silicate melt inclusions, a rare feature in hydrothermal veins. Their composition determined by LA-ICP-MS analysis indicates that the mineralizing fluids, potentially sourced from intermediate magma recharges, have circulated in a magma reservoir in which the residual interstitial melt was more evolved than the melt trapped as inclusions in the magmatic quartz. The combined geochemical and geochronological data obtained show that several episodes of rejuvenation of a highly crystallized upper-crustal silicic magma reservoir, probably triggered by intermediate magma recharges and by circulation of CO2- and S-rich fluids exsolved from them, are at the origin of the large diatreme-dome complex and porphyry-type mineralization events at Cerro de Pasco.

Lithogeochemistry of hydrothermally-altered host rocks by multiple mineralizations in the Mankayan Mineral District, Philippines

The overprinting episodes of porphyry-type and epithermal-type mineralization in the Mankayan District, northern Luzon, Philippines allow an investigation on variation of geochemical signatures with different alteration assemblages. Due to the multiple hydrothermal activities in Mankayan, some older porphyry-type deposits have been overprinted by acid-sulfate alteration that is commonly associated with high-sulfidation epithermal mineralization. In this study, we analyzed metavolcanic basement rocks and dioritic rocks that host porphyry-type mineralization in the Far Southeast deposit, Honeycomb prospect and Christine prospect, which all have near-neutral pH alteration assemblage of illite/muscovite + chlorite ± quartz. We compared their geochemical data with those of the Fatima porphyry deposit, which was overprinted by quartz + alunite ± kaolinite/dickite alteration. Furthermore, we also compared the geochemical data of the metavolcanic and dioritic rocks in the Carmen and Florence prospects hosting quartz-pyrite-gold and enargite veins which overprinted earlier porphyry-type mineralization. N-MORB-normalized multi-element diagrams show that the host rocks preserve negative anomalies of high field strength elements (HFSEs) that are typical of magmas generated in a supra-subduction zone setting. The non-mineralized metavolcanic and dioritic rocks show variable signature of the large ion lithophiles (LILEs), while the altered metavolcanic and dioritic rocks show a more consistent signature. Negative anomaly of Rb is associated with acid-sulfate alteration, while positive anomaly of Rb was observed in the dioritic rocks that have been altered by near-neutral pH fluids. Furthermore, acid-sulfate alteration significantly added LREEs and depleted HREEs compared to the near-neutral pH alteration.Mass changes in altered rocks were determined using the isocon technique. Mass changes are generally more pronounced in the acid-sulfate altered rocks compared to the near-neutral pH altered rocks. The metavolcanic rocks altered to quartz + alunite in Carmen and Florence significantly gained SiO2, Al2O3 and S, and lost Na2O, CaO, MgO and Fe2O3. The dioritic and metavolcanic rocks altered to chlorite + illite in the Far Southeast, Honeycomb, Christine and Fatima porphyry deposits lost SiO2 and Al2O3, while the concentrations of other elements remain relatively unchanged.The pH-dependence of the geochemical behavior of Rb in hydrothermal conditions was utilized to construct new molar element ratios that could differentiate the rocks that underwent K-metasomatism either under near-neutral pH or acidic conditions. The recognition of this behavior could be useful in a routine lithogeochemical analysis that is being used in exploration.

Two episodes of REEs mineralization at the Sin Quyen IOCG deposit, NW Vietnam

The Sin Quyen iron oxide-copper–gold (IOCG) deposit in northwestern Vietnam contains a proven reserve of 52.8 Mt ores at 14% Fe, 0.91% Cu, 0.7% REEs (rare earth elements), and 0.44 g/t Au. REEs mineralization is hosted within Ca-silicate alteration zone and associated with Fe-Cu ore bodies in the gneiss, mica schist, and marble of the Upper Sin Quyen Formation. Two mineralization episodes are identified based on the field and petrographic relations. The first episode includes sodic alteration (stage I-1), calcic alteration and associated REE mineralization (stage I-2), and localized K-Fe alteration (stage I-3). The second episode is main stage mineralization and contains four main stages of alteration: pre-ore Na alteration (stage II-1), Ca-Fe alteration and the associated Fe-REE mineralization (stage II-2), K-Fe alteration and associated Cu-Au mineralization (stage II-3), and the final carbonate stage of quartz-carbonate veins (stage II-4) crosscutting the above-mentioned alteration phases and ores.Primary allanite and type 1 titanite (Tnt-1) from episode 1 yield weighted mean 206Pb/238U ages of 882 ± 3 Ma and 881 ± 8 Ma (2σ), respectively, which are interpreted as the timing of REE mineralization in episode 1. Secondary allanite and type 2 titanite (Tnt-2) associated with iron-oxide and Cu-Au ores, however, have U-Pb ages of 840 ± 7 Ma and 838 ± 5 Ma (2σ), respectively. These ages are hence considered to represent the timing of polymetallic IOCG mineralization in episode 2. ~880 Ma titanite grains have εNd(t) values ranging from −7.00 to −5.43, which are intermediate between the Neoproterozoic felsic intrusions and ore-hosting meta-sedimentary rocks in the region and likely reflect interaction between magmatic fluids and ore-hosting rocks. In contrast, ~840 Ma titanite have εNd(t) values ranging from −4.31 to −1.97, similar to those of the Neoproterozoic felsic intrusions, indicating a possible magmatic fluid source for the episode II IOCG mineralization. Multiple episodes of mineralization at Sin Quyen were likely formed during the prolonged tectonothermal events related to backarc extension during the Neoproterozoic subduction along the western margin of the Yangtze Block.

Multiple episodes of gold mineralization in the East Kunlun Orogen, western Central Orogenic Belt, China: Constraints from Re-Os sulfide geochronology

The Gouli goldfield (>110 t Au), located in the East Kunlun Orogen, western Central Orogenic Belt of China, is one of the most important goldfields in this area. In the last decade, a number of orogenic gold deposits (e.g., Guoluolongwa and Annage) have been shown to be hosted by rock units of different lithology and ages. Rhenium-osmium (Re-Os) geochronology of sulfides from gold-bearing veins was performed to define the chronologic relationships between gold mineralization present in the metamorphic rocks (Proterozoic and Silurian) of the East Kunlun Orogen. Sulfides (pyrite and chalcopyrite) from pyrite-quartz vein and polymetallic sulfides-quartz vein in the Guoluolongwa gold deposit yield Re-Os isochron dates of 374 ± 15 Ma (MSWD = 4.6; initial 187Os/188Os ratio (Osi) = 0.06 ± 0.22) and 354 ± 7 Ma (MSWD = 0.18; Osi = 0.13 ± 0.01), respectively. Similar ages are also revealed by the pyrite mineral separates from the Annage gold deposit (383 ± 8 Ma and 349 ± 6 Ma). These ages are interpreted to record the timings of the formation of the two vein types in these deposits, which are nominally separated by ~20 Ma.The new Re-Os ages presented here identify the first two Late Paleozoic (Devonian and Early Carboniferous) gold-mineralizing events in the East Kunlun Orogen and thus indicate at least two mineralization epochs in this area given ages (Late Triassic) of other gold systems and field observations. Considering the geological background and temporal distribution of gold deposits in adjacent areas (western Qinling and Qaidam-Qilian), we suggest that gold deposits in the western Central Orogenic Belt were formed in collisional/post-collisional settings being controlled by common tectonic-magmatic activities related to the evolution of both the Prototethys Ocean (Proterozoic – Paleozoic) and Paleotethys Ocean (Paleozoic – Early Cenozoic).Further, the initial Os (Osi) obtained from the Re-Os isochron suggest that for the two vein types in the Guoluolongwa gold deposit the Os and by inference the ore metal (Au) were derived from a mantle-like source (Osi values = ~0.12–0.13), which should be related to the contemporaneous mantle-like magmatism. In contrast, the pyrite-quartz vein in the Annage gold deposit possesses a significantly radiogenic Osi value (3.65 ± 0.51). Given the similar timing of mineralization between the Guoluolongwa and Annage deposits, it is considered that the ore metal likely has a similar origin, i.e., a mantle-like source, however at Annage the hydrothermal fluid interacted with the Proterozoic metamorphic host rocks and leached radiogenic Os that masks any evidence of a mantle-like source.

Fluid properties and origins of the Lannigou Carlin-type gold deposit, SW China: Evidence from SHRIMP oxygen isotopes and LA-ICP-MS trace element compositions of hydrothermal quartz

Oxygen isotope and trace elements characteristics of ore-related quartz from Lannigou gold deposit, a typical fault-control second largest Carlin-type Au deposit in SW China, provide valuable information about the properties and origins of the ore-forming fluids. Previous works has focused on vein quartz instead of ore-related jasperoid-like quartz grain due to hard separation. Based upon different cathodoluminescence (CL) textural patterns and intensities observed within the quartz, four generations of quartz from this deposit were identified: Quartz I is sedimentary detrital quartz; Quartz II is syn-mineralization jasperoid-like quartz intergrown with and/or containing fine (<10 μm) As-bearing pyrite and arsenopyrite; Quartz III is late-mineralization veinlet quartz with a small of medium-coarse-grained (about 50–100 μm) As-bearing pyrite; and Quartz IV is the post-mineralization drusy thick-veined quartz. Analyses by sensitive high-resolution ion microprobe (SHRIMP) and laser ablation inductively coupled mass spectrometry (LA-ICP-MS) were used to determine O isotope and trace elements compositions of quartz formed in different stages. The trace elemental (e.g., Al, Li, Ge, Ti) variation of quartz from Quartz II to IV reflect the effects of fluid saturation in CO2 as the result of decarbonization reactions, followed by a progressive fall in CO2, whereas the fluid pH and intensity of argillic alteration increase, progressively. The range of δ18OVSMOW values in Quartz II (12.1–24.8‰) is wide but narrows in Quartz III (24.1–27.8‰) and IV (24.3–26.9‰). The estimated fluid δ18O values of early- or main-stage (calculated from Quartz II) is 3.2–15.9‰, the late-stage (calculated from Quartz III) is 12.5–16.2‰, and the post-stage (calculated from Quartz IV) is 9.0–11.5‰. It is suggested that the ore-forming fluids of Lannigou gold deposit reflect a mixed source: a low O isotope end-member that was magmatic- or basement related, whereas the high O isotope end-member may have been fluid interacted with wall-rock, whose influence strengthened during the mineralization episode. The narrow δ18OVSMOW ranges of Quartz III and IV also suggest that any meteoric water influence on the late hydrothermal system was weak.

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

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

Gold metallogeny of the northern Capricorn Orogen: The relationship between crustal architecture, fault reactivation and hydrothermal fluid flow

The timing and distribution of gold mineralization in Proterozoic orogens is influenced by crustal architecture which is often established long before gold mineralization occurs. Gold occurrences in such settings are commonly associated with crustal-scale faults formed at cratonic margins. Once established, these faults provide critical pathways for hydrothermal and mineralizing fluids which during repeated fault reactivations can result in remobilization or introduction of new auriferous fluids resulting in overprinting gold events. Recently published geochronological data for the northern part of the Proterozoic Capricorn Orogen in Western Australia show it has experienced at least three episodes of gold mineralization occurring at c. 2400, 1770 and 1680 Ma. This information, combined with new data directly linking the timing of hydrothermal activity, gold mineralization and fault reactivation show that the crustal-scale Nanjilgardy and Baring Downs Faults, and their subsidiary structures, were (re)activated during discrete orogenic events. Many of the gold deposits are associated with intracratonic reworking during the 1820–1770 Ma Capricorn Orogeny and 1680–1620 Ma Mangaroon Orogeny. Intracratonic settings are not normally considered prospective for gold mineralization due to a lack of input of juvenile material. However, it appears that repeated hydrothermal fluid flow during intracratonic events, has the potential to upgrade gold mineralization or increase gold endowment throughout the orogen, either through gold remobilization or through introduction of new gold, increasing the potential for economic gold deposits.

New zircon fission track analysis constraints on tectonic-mineralization epochs in the Ganzi-Litang gold belt, eastern Qinghai-Tibet plateau

The Ganzi-Litang gold belt, as a part of the Sanjiang Tethys orogen, is located between the Yidun block and Songpan-Ganzi Block/Terrane in the eastern Qinghai-Tibetan plateau and experienced oceanic slab subduction, continent-arc collision and intracontinental convergence since the Indosinian orogeny. A series of gold ore deposits have been found within the region. This paper describes the tectonic evolution and episodes of gold mineralization within this belt using zircon fission track (FT) thermochronology. A total of 15 zircon FT analysis results were obtained that can be divided into four age groups (217–213 Ma, 190–160 Ma, 155–93 Ma and 72–67 Ma) representing four distinct episodes of gold mineralization, of which the middle two episodes predominate. Eruption of the auriferous volcanic rocks that comprise the belt started at 217–213 Ma when the Ganzi-Litang Meso-Tethys ocean began to subduct. The mineralization episode at 190–160 Ma corresponds to the formation of auriferous volcanic rocks during intracontinental collisional-convergence of the Ganzi-Litang belt. Finally, the episodes at 155–93 Ma and 72–67 Ma are respectively related to the closing times of the Bangong-Nujiang and Yarlung Zangbu oceans, corresponding to tectonic quiet episodes.

Fluid pressure–dominated orogenic gold mineralization under low differential stress: case of the Yaouré gold camp, Côte d’Ivoire, West Africa

The ~ 1.5 Moz Yaoure gold deposit, which is located within the Birimian greenstone belts of central Cote d’Ivoire (West Africa), is associated with two stages of economic gold mineralization. Both ore-forming stages occurred during protracted E-W-directed shortening associated with the Eburnean orogeny. The first mineralization stage is hosted by fault-fill veins along conjugate ENE-striking (dextral) and WNW-striking (sinistral) strike-slip fault arrays. This ore stage is associated with a polymetallic assemblage including Mo, Bi, Pb, W, Te, Ag, and Au and cryptic alteration in wall rocks. The second and main gold mineralization stage is associated with a low-displacement fault-fracture-vein mesh formed during a reverse faulting episode. This second gold phase is associated with a polymetallic assemblage including W and Au ± Pb and is characterized by pronounced albite-ankerite-pyrite hydrothermal alteration in wall rocks. Shear veins associated with this second mineralization episode formed during episodic fluid pressure variations under low differential stress within pre-existing low-angle reverse fault planes. Permeability destruction by albite-ankerite-pyrite hydrothermal sealing of these low-angle reverse faults resulted in fluid pressure build-up and ultimately in the development of extension veins under low differential stress in the late stages of the structural evolution of the deposit. This study presents the structural evolution of a polyphase orogenic gold deposit and highlights that the interplay between fault zone activity, hydrothermal alteration, and fluid pressure fluctuations at low differential and deviatoric stresses were key in controlling fluid flow and the formation of ore within optimally-oriented faults.

Multiple episodes of Late Paleozoic Cu-Au mineralization in the Chatkal-Kurama terrane: New constraints from the Kuru-Tegerek and Bozymchak skarn deposits, Kyrgyzstan

The Chatkal-Kurama terrane is the most fertile region for porphyry-skarn Cu-Au mineralization (~31 Mt Cu and 2300 t Au) in the West Tianshan, even though in the Chatkal range of Kyrgyzstan only limited studies have been conducted. We present the first robust geochronological and geochemical data for the important Kuru-Tegerek and Bozymchak skarn Cu-Au mineralization and related magmatism in the Chatkal region. Consistent zircon SHRIMP U-Pb and molybdenite Re-Os ages reveal that the Kuru-Tegerek skarn Cu-Au deposit formed at about 325 Ma (zircon U-Pb, 326 ± 3 Ma; molybdenite Re-Os, 323 ± 2 Ma), and the Bozymchak skarn Cu-Au deposit formed at about 305 Ma (zircon U-Pb, 304 ± 2 Ma; molybdenite Re-Os, 305 ± 3 Ma). The new ages, in combination with previous data, suggest four pulses of Cu-Au mineralization and related magmatic events in response to changing dynamic settings. The ca. 325 Ma Kuru-Tegerek in the NE Chatkal is associated with low- to medium-K calc-alkaline tonalite porphyry derived from Precambrian continental crust (εNdt = −16.3 to −20.0, T2DM = 2.4–2.7 Ga) in an early subduction stage. The ca. 315 Ma time slice records the peak of tremendous porphyry Cu-Au mineralization (Kal’makyr and Sarycheku) and voluminous magmatism with high-K calc-alkaline to shoshonite series rocks of mixed origin of continental crust and metasomatized mantle-derived that denote a compressive regime due to flat subduction. The ca. 305 Ma Bozymchak Cu-Au skarn deposit is also associated with a high-K calc-alkaline intrusion (granodiorite porphyry) and supposedly marks the cessation of supra-subduction magmatism. The Early Permian Kochbulak high sulfidation epithermal Au deposit is related to a stratovolcano setting that is closely associated with post-collisional shoshonitic rocks related to slab breakoff. Collectively, the Cu-Au mineralization in the Chatkal-Kurama terrane formed during a 30 My period related to multiple magmatic pulses in a geodynamic setting evolving from early over peak to late subduction to post-collisional slab breakoff.

Overprinting by episodic mineralization in the Dongyaozhuang gold deposit, Wutai Mountain, China: Constraints from geology, mineralogy, and fluid inclusions

The Archean volcanic‐sedimentary rocks (greenstones) hosting the Dongyaozhuang (DYZ) gold deposit are situated in the Wutai Mountain, north‐central China. Field geology and mineral assemblages show at least two episodes of mineralization. The first episode features deformed quartz‐pyrite veins filling in the regional foliation (MI, Paleoproterozoic) and can be divided into two stages (MIa and MIb) based on whether the mineralization is accompanied by tourmalinization. The mineral assemblages are mainly quartz + carbonate + pyrite + chalcopyrite (+ tourmaline for MIb); both are cut by deformed barren quartz veins, which represent the final stage of MI. The second episode features undeformed stockworks/veinlets with a mineral assemblage of quartz + carbonate + pyrite + chalcopyrite + arsenopyrite ± native gold (MIIa), crosscutting MI; these ore bodies are also cut through by undeformed barren carbonate and/or quartz veins (MIIb), which represent the end of metallogeny. By integrating the crustal evolution history with ore geology, we suggest that the DYZ gold deposit is a product by overprinting of episodic mineralization rather than a single metallogenic event. For further understanding and evidence in support of this speculation, fluid inclusions and hydrothermal chlorite and biotite were studied to reveal the physicochemical conditions of fluids from various stages, and C‐H‐O isotopes were used to trace the source(s) of fluids. Temperatures recorded in chlorite from various stages C1 (from the MIa), C2 (MIb), and C3 (MIIa) generally agrees with the homogenization temperatures of aqueous type fluid inclusions (FIs) of corresponding stages. Components of FIs from each stage are dominated by water with low salinities (0–12.6 wt% NaCl equiv). The Ib‐1, Ib‐2, and Ib‐s type CO2‐H2O FIs observed from the same deformed quartz vein of the MIb can be attributed to overprinting of hydrothermal fluids. The primary Ib‐1 and Ib‐2 FIs (209–404°C) were trapped at pressures of approximately 2.2–3.7 kbar, representing the formation pressure of the MI stage, whereas the secondary Ib‐s FIs (240–349°C) were trapped at pressures of approximately 0.8–1.5 kbar, which indicates overprinting induced by MII. The C‐H‐O isotope compositions of quartz and carbonates from MIa, MIb, and MIIa can be interpreted to indicate that the fluids were derived from the same source with multistage evolution or to reflect a homogeneous signature induced with overprinting mineralization. According to the geology, mineral assemblages, component of fluid inclusions, and C‐H‐O isotopes, the DYZ gold deposit is likely to be a product of overprinting of an orogenic gold deposit.

Fluid evolution of the Wushan skarn-dominant copper deposit in the Middle-Lower Yangtze River metallogenic belt, Eastern China

The Wushan copper skarn deposit (1.37 Mt at 1.17% Cu) is located in the Middle-Lower Yangtze River polymetallic belt. Skarn orebodies mainly occur in the Carboniferous and Permian carbonates adjacent to Early Cretaceous granodiorite porphyries (148–138 Ma). Ore deposition underwent two episodes of metallogenic events, involving hydrothermal evolution followed by skarn formation and porphyry-related mineralization. The skarn episode formed massive, disseminated, veinlet- and breccia-style mineralization at the contact zone, whereas porphyry mineralization is characterized as disseminated and veinlet-style only. Various types of fluid inclusions (daughter mineral-bearing, CO2-bearing, vapor and aqueous–vapor) are classified based on their fluid composition and phase assemblages.The hydrothermal fluids are mainly derived from a magmatic origin, which exsolves during the melt-fluid differentiation. Primary fluid in endoskarn is interpreted as representing two immiscible phases evolving from a low-salinity initial fluid. The initial supersaturated fluid has a relative low salinity and the wide range of Th values (433–626 °C) implies heterogeneous trapping, corresponding to pressures of 371–646 bars and hydrostatic depth of 3.7–6.5 km. Primary fluid inclusions trapped in syn-ore quartz show the coexistence of S-type inclusions (~30.0 wt% NaCl equiv) with vapor-rich and liquid-rich inclusions, indicating fluid immiscibility and phase separation from heterogeneous trapping. The homogenization temperatures (347–434 °C) of primary vapor-rich inclusions represent the trapping temperatures, corresponding the trapped pressures range from 152 to 374 bars and a hydrostatic depth of 1.5–3.7 km. Copper mineralization in episode porphyry occurs on a very small scale and have a clear trend of decreasing temperatures and salinities during fluid evolution. A similar scenario occurred during the porphyry episode in which fluid immiscibility led to copper mineralization.Significant trends of decreasing temperatures and salinities for both mineralization episodes reflect the change from a magmatic fluid-dominated system to a mixed source fluid that incorporated formation water from the country rocks and/or meteoric water. Controlled by the chemical transition of the fluid, this mixing process produced a relatively cool fluid system with lower salinities, which enhanced the precipitation of Cu–Fe sulfides. H–O–C isotope signatures further indicate that both the fluid and metal are predominantly derived from magmatic sources, and that multiple fluid pulses contributed to form skarn minerals and sulfides in the Wushan deposit.

The Sr–He–Ar isotopic and elemental evidence constraints on the ore genesis of the Zhaxikang Sb–Pb–Zn–Ag deposit in southern Tibet

The genesis of Zhaxikang deposit is still debated, and three main geological environments have been proposed to model the mineralization: hot spring, magmatic hydrothermal fluid, and sedimentary exhalative (SEDEX) overprinted by hydrothermal fluid. This study presents elemental and Sr–He–Ar isotopic data of minerals from different mineralization stages to support the genetic model of earlier submarine hydrothermal sedimentation (metasomatism) metallogenesis superimposed by a later magmatic‐hydrothermal fluid. The linear relations between 1/Sr and 87Sr/86Sr ratios, Sr isotopic two‐component mixing model and elemental characteristics for Mn–Fe carbonate (87Sr/86Sr ratios: 0.713135–0.720277, Sr concentrations: 0.72–6.05 ppm) and calcite (87Sr/86Sr ratios: 0.707953–0.716116, Sr concentrations: 177–1,194 ppm) imply that the first episode of mineralization relates to a seafloor hydrothermal fluid and the second episode of mineralization is associated with a magmatic hydrothermal fluid. Furthermore, noticeable different He–Ar isotopic characteristics of the two episodes of mineralization (the first episode: 40Ar/4He: 0.06–0.27, 40Ar/36Ar: 288.9–1483.4, 38Ar/36Ar: 0.16–0.22, 3He/4He: 0.04–0.08Ra; the second episode: 40Ar/4He: 0.23–211.76, 40Ar/36Ar: 831.5–10047, 38Ar/36Ar: 0.17–0.25, 3He/4He: 0.04–1.31Ra) indicate that both these two episodes of ore‐forming fluids are mainly crustal‐derived with a more possibly magmatic hydrothermal origin for the second episode. Overall, the elemental and Sr–He–Ar isotopic data demonstrate the existence of two episodes of mineralization in which the initial submarine hydrothermal sedimentation (metasomatism) metallogenesis was overprinted by a later magmatic hydrothermal fluid.

Two episodes of REE mineralization in the Qinling Orogenic Belt, Central China: in-situ U-Th-Pb dating of bastnäsite and monazite

Recent exploration revealed a number of rare earth element (REE) deposits that are distributed along the Qinling Orogenic Belt, Central China. These deposits have an estimated total reserve of about 2 Mt. REE2O3, thus making this belt a world-class REE metallogenic province. Understanding the metallogenesis of the belt requires direct dating of REE minerals. In this study, LA-ICP-MS U-Th-Pb dating on bastnasite and monazite from the Huangshuian, Taipingzhen, and Miaoya deposits in different units of the belt was used to precisely determine the timing of the REE mineralization. The Huangshuian deposit in the north is a carbonatite-related Mo-(REE) deposit in which the REE minerals are closely associated with molybdenite. After correction for common Pb and excessed 206Pb decayed from 230Th, a weighted average 206Pb/238U age of 207 ± 4 Ma (n = 17; MSWD = 1.9) is obtained for bastnasite grains from this deposit. Such an age is slightly younger than that of the final collision (peak at 230–220 Ma) of the Qinling Orogenic Belt, thus indicating that the Mo-REE mineralization is likely related to a post-collisional extension setting. The Taipingzhen REE deposit in the middle contains sheet-like ore bodies composed of veins where bastnasite, the dominant REE mineral, is closely associated with quartz, fluorite, and barite. In situ bastnasite U-Th-Pb dating shows that the REE mineralization in this deposit has formed at 421 ± 7 Ma (n = 17; MSWD = 1.5), synchronous with extension-related magmatism in the region. The Miaoya deposit in the south is the largest one in the belt, and it is essentially a REE-mineralized syenite-carbonatite complex. In this deposit, the monazite grains are closely associated with major minerals of the syenites or carbonatites (e.g., K-feldspar or calcite), but commonly exhibit complex internal textures. Different domains of monazite yield two groups of U-Pb ages at 414 ± 11 Ma (n = 5; MSWD = 0.91) and 231 ± 2 Ma (n = 21; MSWD = 3.1), whereas the bastnasite has an age of 206 ± 4 Ma (n = 14; MSWD = 1.5). The early age of 414 Ma is obtained from homogenous monazite grains and in good agreement with zircon U-Pb ages of the Miaoya syenite-carbonatite complex, and thus is considered to represent the timing of the major REE mineralization in the deposit. The younger ages of 231–206 Ma are obtained from monazite grains with complex internal textures and bastnasite in late veinlets, thus recording secondary, consecutive REE remobilization events likely related to the compression process during formation of the Qinling Orogenic Belt. Our new U-Th-Pb ages, in combination with previously geochronological data, demonstrate that there are two episodes of REE mineralization at 440–410 Ma and 220–200 Ma in the Qinling Orogenic Belt.

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.