Sericitic Alteration Research Articles

Phase separation and fluid mixing revealed by trace element signatures in pyrite from porphyry systems

Porphyry deposits host various trace elements in economic amounts, but the hydrothermal processes causing their fractionation and enrichment are still not fully understood, but vital to target the most prospective mineralisation. We present the first micro-analytical study on the trace element composition of pyrite from the Koloula Cu-Au porphyry in the young and thin (<25 km) Solomon Islands arc. A statistical evaluation of the trace element data of pyrite indicates that mineral inclusions obscure the chemical signature of the mineralisation processes. The filtered pyrite data, from which the inclusions were excluded, correlate with variations in temperature and salinity, as defined by fluid inclusions from several alteration zones. Trace element ratios in pyrite show systematic variations with fluid temperature and salinity (Co/Ni, Se/Te), phase separation (Co/Ni, Co/As) and mixing of magmatic fluids and meteoric waters (Se/Ge). The mineralisation in the potassic alteration zone was controlled by the formation of a hypersaline liquid (Co/As > 1, Co/Ni > 50) from a magma-derived fluid (Se/Ge ~ 100) at lithostatic pressure conditions and temperatures of up to 700 °C (Se/Te > 50). This was followed by a transition to hydrostatic pressure conditions due to open-fracture continuity towards the paleo-surface, marking the onset of boiling in the chlorite-sericite to sericitic alteration zone (Co/As < 1), where minor proportions of meteoric water were involved (Se/Ge < 100). The shallowest part of the mineralisation is controlled by lower temperature (<300 °C, Se/Te < 50) vapour-rich fluids (Co/As < 1) that condensed into meteoric waters in an epithermal transition zone (Co/Ni < 50, Se/Ge < 100). Trace element systematics in pyrite from progressive alteration zones therefore preserve the time-space evolution of porphyry (-epithermal) systems in young and thin oceanic island arcs.

Towards the fertility trend: Unraveling the economic potential of igneous suites through whole-rock and zircon geochemistry (example from the Tapajós mineral Province, Northern Brazil)

Magmatic hydrothermal mineral deposits axiomatically frame the hosting pluton and the given tectonic setting in which they are inserted. Unsurprisingly, pre-Cambrian porphyry deposits are different than Phanerozoic examples, as collisional or post-collisional deposits are different than arc-related mineralizing systems. As such, this contribution assesses the tectonic framework and the magmatic evolution of the igneous suites present in south-central Amazonian Craton (Tapajós Mineral Province, TMP), and how these parameters translate into metallogenetic potential for the formation of magmatic-hydrothermal copper and gold deposits. For this purpose we gathered whole-rock geochemistry data from selected TMP copper and gold deposits and present new in situ trace-element and U-Pb analyses in zircon grains.The host rocks of the selected mineralizing systems belong either to the older magmatic sequence (OMS, 2.00–1.95 Ga), or to the younger magmatic sequence (YMS, 1.90–1.86 Ga). Whereas OMS presents characteristics of arc-related rocks, YMS represents the evolution towards post-orogenic or collisional setting. OMS might be divided into groups I, II and III granitoids. Group I comprises granites and granodiorites that mark the onset of the arc-magmatism in the TMP at ca. 2011 Ma. In this stage rocks are peraluminous, ferroan, anhydrous, show a strong crustal component and fO2 values close to or below the fayalite-magnetite-quartz buffer (ΔFMQ), yielding metallogenetic unfertile pluton. These rocks correlate with the Cuiú-Cuiú Complex and comprise samples from the Patrocínio and Tocantinzinho deposits. Group II granitoids correlate with the Creporizão Suite and comprise Tocantinzinho, São Jorge, Chapéu do Sol and Patrocínio deposit samples (with extrusive equivalents in the Coringa deposit). Rocks are metaluminous to peraluminous, magnesian to ferroan and mark the evolution of the magmatism towards more oxidizing (0 ≤ ΔFMQ ≤ + 4), hydrous and metallogenetically fertile conditions at ca. 1986 Ma. Mineralized zones are defined by gold bearing sulfide veins and veinlets within the potassic or sericitic alteration halos. Group III comprises rarer high-K, metaluminous, ferroan, anhydrous and reduced syenites and monzonites dated at 1993 and 1974 Ma, generated by decompression melting of metasomatized mantle. By itself, group III rocks should be considered as unfertile batches of magma, however, its interaction with the coeval, more hydrous and oxidized group II melts, confer these magmas their metallogenetic potential. Mineralization in group III rocks is defined by disseminated pyrrhotite – pyrite ± gold within the sericitic, chloritic and/or carbonate alteration zones.YMS comprises intermediate and acid rocks that belong to the Parauari Intrusive Suite and to the Iriri Group. Whereas, intermediate volcanics from YMS evolved on a hydrous and reduced petrologic trend, acid volcanics and the Batalha and Palito granitoids evolved on a dry and reduced trend, reflecting a change on TMP’s tectonic context, from magmatic-arc to a post-orogenic or collisional tectonic setting. Despite the reduced and anhydrous characteristic of the magmas, YMS’s metallogenetic potential is related with remobilization or melting of SCLM or lower crustal Au-rich sulfides formed on the previous magmatic events. Hence, the first pulses of the YMS might be considered as potentially fertile for the formation of Au-rich magmatic-hydrothermal deposits.

Mineralogická charakteristika sekundárních změn miocenních vulkanoklastických hornin z jižní a střední Moravy (Česká republika)

Bentonite is a significant industrial raw material which deposits deserve protection. The initiative for elaborating this study was the decision from November 2019 of the current owner (the town of Ivančice) to remediate the entire area of the deposit Ivančice-Réna. Lower Miocene volcaniclastic rocks from the Ivančice-Réna (Ivančice) and Middle Miocene sediments in surrounding area of Lipník nad Bečvou are relatively rich in clay minerals (smectites). The mineralogical characteristics of the volcaniclastic rocks were examined using several methods: polarized-light microscopy, X-ray powder diffractometry (XRD), electron microprobe (SEM–WDX), and whole-rocks chemical analysis (ICP-MS). Acid ash-fall tuff and/or very fine-grained tuffite form layers with variable thickness (several cm to m). Grains larger than clay fraction are formed by K-feldspars, plagioclase, biotite, muscovite and quartz crystals accompanied by fragments of pumice and glass shards. The whole-rocks chemical composition of the investigated volcaniclastic rocks indicates similar magmatic sources for both examined samples (Y = 28 and 29 ppm, Yb = 2.8 and 3.2 ppm, Nb = 12 and 14 ppm, Ta = 1.1 and 1.2 ppm, Zr/Ti = 0.16 and 0.17 and Nb/Y = 0.4 and 0.5). The formation of smectite from alteration of rhyolite volcanic glass is accompanied by an increased loss on ignition (LOI: 9.4 and 20.2 wt. %) together with a decrease in K2O (0.7 and 2.1 wt. %) and Na2O (0.6 and 2.1 wt. %). The absence of a negative Ce anomaly suggests that secondary alterations took place under suboxic or anoxic conditions. Smectite and minor opal partially replace volcanic glass and pumice shards. Plagioclase (Ab59–60) and K-feldspar (Or62–78 Ab21–33 An0–1) crystals are relatively fresh (weak sericitic alteration). Biotite is partly to wholly oxidized and chloritized (4.9–6.2 wt. % K2O). Iron oxyhydroxides are present only as minor components. Variation of intensity of secondary alteration (bentonitization) within the studied volcanoclastic layer from the Ivančice-Réna suggests sedimentation in lacustrine environment. In contrast to the case of the sample from Lipník nad Bečvou, the smectite was formed authigenetically from volcanic glass in interaction with seawater or during an early diagenetic process.

Three-Dimensional Audio-Magnetotelluric Imaging including Surface Topography of the Cimabanshuo Porphyry Copper Deposit, Tibet

Cimabanshuo deposit is a newly discovered porphyry copper (Cu) deposit with giant metallogenic potential, found in the western segment of the Gangdese metallogenic belt, Tibet. The average elevation of the deposit is greater than 5500 m and the terrain on which it is found is steep and complex. Therefore, it is untraversed, and the existing exploration works on it are weak. We used 59 AMT sites belonging to an array covering the main, proven mineralization zone and ore bodies of this deposit for an analysis of its underground electrical structure. Dimensionality and strike analysis revealed the apparent three-dimensional (3D) features near the Cu ore bodies. 3D inversion with topography was conducted for the AMT array data. A large range of high-resistivity anomaly (~500–2000 Ωm) appears beneath the proven Cu mineralization zone and ore bodies, which is interpreted as intrusive rocks with potassic alteration. Although containing chalcopyrite, it is characterized by middle–high resistivity due to a low sulfide content and poor connectivity. Moreover, a series of scattered conductors (~10–300 Ωm) around the Cu ore bodies are distributed in the shallow layer from near the surface to ~200 m, possibly indicating phyllic alteration containing pyritization and connected metal sulfides. The proven ore bodies of Cimabanshuo are mainly located at the junction regions between high-resistivity intrusive rocks and high-conductivity sericitization alteration zones. According to this research, the 3D inversion with topography of AMT data can visually display the 3D distribution of intrusive rocks and alteration zones beneath porphyry Cu deposits in high-elevation regions, and provides a reference for further exploration works.

In-situ S–Pb isotopic and trace elemental compositions of sulfides from the Habo Au polymetallic deposit: Evidences for vein-type Au mineralization in the Ailaoshan Au belt

The Habo Au polymetallic deposit is located in the south of the Ailaoshan-Red River tectonic zone. Mineralization is controlled by a strike-slip fault, which was intruded by aplite. Ore minerals are dominated by pyrite and arsenopyrite. Gold is invisibly and ionically bound in pyrite and arsenopyrite. Three hydrothermal alteration-mineralization stages can be identified: quartz-pyrite (py1) ± arsenopyrite vein associated with sericite alteration (I), quartz-pyrite (py2)-polysulfide (II) and quartz-calcite (III). The aplite yielded zircon U − Pb ages of ca. 35.4 Ma while the sericite in pyritized siltstone yielded an Ar-Ar age of ca. 37.5 Ma, constraining the mineralizing age. In situ S–Pb isotopic compositions for sulfides were measured by fs-LA-MC-ICP-MS. Sulfides from the deposit show uniform δ34S values ranging from –5.1‰ to + 2.5‰, a typical characteristic of magmatic-derived S. Pb isotopic compositions of galena are similar to those of the granite in the Habo granite complex, suggesting that the metal is probably sourced from the Habo granite complex. In-situ LA-ICP-MS spot analysis indicates that py1 has high Ni, Co, As and Se concentrations while py2 contains higher concentrations of Au, As, Cu, Pb and Zn. These characters reveal that the ore-forming fluids are As-rich and largely unsaturated with respect to Au. Based on the ore deposit geology, dating and isotopic data, the Habo Au polymetallic deposit mineralization is similar to typical intrusion-related vein-type deposit, formed by fluids originated from magma differentiations of the Habo granite complex.

Evidence of gas plume model in porphyry copper deposits based on anatomy, fluid inclusions and H-O isotopes: Insight from Kahang deposit, Iran

The Kahang deposit (100 Mt at 0.6% Cu) is one of the important porphyry copper deposits in the central part of Urumieh-Dokhtar Magmatic Arc (UDMA), Iran. The mineralization occurs as chalcopyrite and molybdenite in quartz and anhydrite -bearing veinlets or breccias and is closely associated with sericitic and phyllic alterations. Through comprehensive studies of the deposit's anatomy, some previously overlooked evidence raised new questions about the ore-forming process in the Kahang deposit. The coexistence of sulfate and sulfide minerals as veinlets and breccias, pore space breccias, could not be justified solely based on a previously introduced concept (i.e., mixing high temperature-high salinity magmatic water with low temperature-low salinity meteoric water). Fluid inclusions were examined in quartz veinlets of the A1, A2, and B types, anhydrite veinlets, and sphalerite of the L type veinlets. There are three types of fluid inclusions: liquid-rich (L-type), vapor-rich (V-type), and hypersaline (H-type). According to microthermometry of fluid inclusions, the fluids associated with anhydrite veinlets have relatively high temperatures (390–495 °C, mean = 455 °C) and low salinities (12.8–20.9 wt% NaCl equiv.) On the contrary, temperatures below 400 °C justified the coexistence of sulfate and sulfide minerals. The low solubility of anhydrite in high-temperature waters, on the other hand, demonstrates the gas–solid reaction of SO2 (g) and plagioclase at such temperatures, as evidenced by fluid inclusions. Additionally, the fluid inclusions in quartz veinlets generated temperatures (290 to >600 °C) higher than those in the majority of other porphyry copper deposits. H-O isotopes indicated that magmatic fluids dominated, and meteoric waters played an insignificant role. These findings and observations supported the formation of the Kahang porphyry copper deposit as a result of a gas plume and the reactions of gas species with plagioclase to form anhydrite and sulfide minerals, as well as the formation of sericitic alteration in the host rock as a novel scenario.

Structural Controls on Iron Oxide Copper-Gold Mineralization and Related Alteration in a Paleoproterozoic Supracrustal Belt: Insights from the Nautanen Deformation Zone and Surroundings, Northern Sweden

Abstract The Nautanen deformation zone in the Gällivare area of northern Sweden is a highly Cu-mineralized, magnetite-rich, large-scale shear zone with a long-lived (~100 m.y.) deformation, hydrothermal alteration, and mineralization history. This composite structure hosts the Aitik porphyry Cu-Au-Ag ± Mo deposit and several Cu-Au ± Fe ± Ag ± Mo occurrences assigned to the iron oxide copper-gold (IOCG) deposit class. The Nautanen deformation zone was a locus for polyphase deformation and intermittent metasomatic-hydrothermal activity that overprinted middle Orosirian (ca. 1.90–1.88 Ga) continental arc-related volcanic-plutonic rocks. The deformation zone is characterized by intense shearing fabrics that form a series of subvertical to moderately W-dipping, NNW-SSE–trending, first-order shear zones with oblique reverse kinematics and related NNE-SSW–oriented second-order shear zones that control hydrothermal alteration patterns and Cu-Au mineralization. Hydrothermal alteration in the study area formed during several phases. Volcanic-volcaniclastic rocks to the east and west of the Nautanen deformation zone display low to moderately intense, pervasive to selectively pervasive (i.e., patchy zones or bands, disseminations) sericite ± feldspar, amphibole + biotite + magnetite ± tourmaline, and K-feldspar + hematite alteration. Both the amphibole + biotite and K-feldspar + hematite associations occur adjacent to NNW- and NE-oriented deformation zones and are locally associated with minor sulfide. Within the deformation zone, a moderate to intense biotite + amphibole + garnet + magnetite + tourmaline + sericite alteration assemblage is typically associated with chalcopyrite + pyrrhotite + pyrite and forms linear and subparallel, mainly NNW-oriented seams, bands, and zones that locally appear to overprint possibly earlier scapolite + sericite ± feldspar alteration. Late-stage epidote ± quartz ± feldspar alteration (retrograde saussuritization) forms selectively pervasive zones and epidote veinlets across the area and is partly related to brittle faulting. A magnetite-amphibole-biotite–rich, penetrative S1 foliation records shortening during early Svecokarelian-related deformation (D1) and can be related to ca. 1.88 to 1.87 Ga arc accretion processes and basin inversion that overlaps with regional peak metamorphism to near mid-amphibolite facies conditions and a potential initial Cu mineralization event. Folding and repeated shearing along the Nautanen deformation zone can be assigned to a second, late-Svecokarelian deformation event (D2 stage, ca. 1.82–1.79 Ga) taking place at a higher crustal level. This D2 deformation phase is related to late-stage accretionary processes active during a transition to a stage of postorogenic collapse, and it was accompanied by abundant, syntectonic intrusions. D2-related magmatism produced high-temperature and low-pressure conditions and represents a regional magmatic-hydrothermal event that controlled the recrystallization/remobilization of magnetite, biotite, and amphibole. Associated shear zone reactivation during D2 favors the utilization of the Nautanen deformation zone as a fluid conduit, which preferentially controlled the siting and formation of epigenetic Cu-Au mineralization with distinctive IOCG characteristics within second-order shear zones.

Geochronology, geochemistry and Sr-Nd-Hf isotopes of the Heihuashan granite porphyry, NE China, and implications for Cu-Mo mineralization

Heihuashan is a newly discovered porphyry Cu-Mo prospect in Heilongjiang Province, northeastern China, with considerable Cu and Mo mineralization. Until now the ages of the Cu-Mo ores and the causative granite porphyry, the magma origin and characteristics, as well as the mineralization potential at depth are still unclear. In this contribution, whole rock geochemical and Sr-Nd isotopic compositions, zircon U-Pb ages and Hf isotopes, and molybdenite Re-Os dating, are presented to constrain the timing of the magmatism and mineralization, and the petrogenesis of the causative intrusion. The results also provide an opportunity for evaluating the potential of the deep Cu-Mo mineralization.Zircon U-Pb dating using LA-ICP-MS yields a crystallization age of 146.4 ± 1.8 Ma for the Heihuashan granite porphyry, which is consistent with the molybdenite Re-Os isochron age of 143.7 ± 3.1 Ma. These results indicate that the porphyry Cu-Mo mineralization at Heihuashan occurred at late Jurassic to early Cretaceous. The whole rockgeochemicaldatasuggest that the ore-related intrusion is mildly peraluminous and belongs to the high-Kcalc-alkalineseries, I-type granitoids. The granite porphyry samples are enriched in Rb, Ba, Th, U, and Sr, but depleted in Nb and Ta, showing typical arc magma affinities. They also have initial 87Sr/86Sr ratios of 0.70546–0.70550 and εNd(t) values between +0.4 and +0.7. The zircon εHf(t) values for the granitic intrusion range from +3.5 to +9.2, with two-stage Hf model ages of 977–614 Ma. The geochemical and Sr-Nd-Hf isotopic compositions suggest that the parental magma was dominantly derived from the slab-metasomatized mantle, which could have mixed with some lower crust components.The Fe2O3/FeO ratios of the Heihuashan granite porphyry are relatively high, ranging from 0.52 to 1.17, indicating a high magmatic oxidation state. This is also supported by the high zircon Ce/Ce*, Eu/Eu* and Ce/Nd ratios (33–2433, 0.22–0.70 and 2.4–44.0, respectively) and the high magmatic ΔFMQ values (+0.1 to +3.5 with an average of +2.1) calculated using the zircon trace elements. The intrusion has relatively high Sr/Y ratios (40–94) and displays negligible Eu anomalies (Eu/Eu* = 0.68–1.07); the zircons from the intrusion have high (Eu/Eu*)/Y (mostly > 0.0001) and (Ce/Nd)/Y ratios (mostly > 0.01), but low Dy/Yb ratios (generally < 0.4). These suggest that the fractionation of hornblende rather than plagioclase is dominant during the magma crystallization, which reveals a high magmatic water content. The above results indicate that the ore-related magma at Heihuashan is oxidized and hydrous, both of which are critical for porphyry Cu-Mo mineralization. The Heihuashan granite porphyry is geochemically similar to other Cu-related intrusions in NE China and also comparable to many porphyry Cu (-Mo) systems worldwide, implying a high Cu-Mo mineralization potential. Considering the surface and shallow levels at Heihuashan are characterized dominantly by sericite alteration, we suggest exploration and drilling focusing on the deeper levels beneath the currently mineralized domains, where major potassic alteration zones, likely associated with more extensive Cu-Mo mineralization, could be discovered.

Gold-and silver-bearing assemblages in the Ann-Mason copper porphyry deposit, Yerington, Nevada

Porphyry deposits are an important source of copper and their value may be upgraded by minor contents of precious metals, if they are extractable. The mechanisms for enrichment of precious and base metals in these systems are not well understood. This study investigates the deportment of trace metals in the Ann-Mason porphyry deposit, including gold, silver, palladium, mercury, lead and bismuth. Petrographic and geochemical data are integrated to characterise the size and habit of minerals, the host mineral assemblages, and their association with alteration assemblages. Ann-Mason is one of several ore deposits hosted by the Yerington batholith in Nevada, and is being assessed for copper extraction from bornite and chalcopyrite ore assemblages, associated with potassic alteration. Mineralisation assemblages at Ann-Mason have been categorised as chalcopyrite-bornite, chalcopyrite-pyrite and pyrite > chalcopyrite zones. Limited two-metre assay data indicates that gold is most closely associated with bornite, although it is found in all three mineralisation zones. Analysis by SEM-EDS shows that trace elements are mostly present as microparticles hosted by sulfide minerals. Of the 438 grains measured, 89% are hosted by a sulfide mineral, with 68% hosted by bornite. Silver is most commonly present as hessite and gold as electrum, hosted by bornite and associated with potassic alteration. Palladium, mercury and bismuth are most commonly observed as telluride and selenide minerals. Palladium minerals are associated with potassic alteration, while mercury and bismuth minerals are mostly found with sericitic alteration. High fineness native gold is observed as three round blebs hosted by pyrite or silicates. Observations suggest that the trace metals in the chalcopyrite-bornite zone may have been incorporated by bornite and chalcopyrite, and exsolved upon cooling. In the chalcopyrite-pyrite and pyrite > chalcopyrite zones, the trace metals may have been deposited directly from a mineralising hydrothermal fluid and incorporated into the growing sulphide minerals. These findings have implications for the paragenesis of porphyry deposits, as well as for the milling processes that would be needed to extract precious metals at the Ann-Mason porphyry deposit.

Application of portable X-ray and micro-X-ray fluorescence spectrometry to characterize alteration and mineralization within various gold deposits hosted in southern New Brunswick, Canada

New Brunswick hosts multiple types of gold deposits related to various stages of Appalachian orogenesis. Some of these structurally controlled deposits are considered intrusion-related; however, the majority have characteristics of orogenic deposits. The geochronology and genesis of the gold and antimony deposits in southern New Brunswick have been studied to varying degrees, but the relationship between mineralization and tectonism remains unresolved. This study involves the examination and comparison of auriferous quartz (-carbonate) veins associated with orogenic and intrusion-related gold mineralization of southern New Brunswick. The Belleisle Bay and Annidale groups (Annidale area) are host to mainly orogenic type gold mineralization, whereas in the Cookson and Mascarene groups (Clarence Stream area), gold mineralization is characterized as intrusion-related. For this study, the Devil Pike Brook deposit and Sheba Pit, East Scotch Settlement BP gold occurrences and the Bald Hill antimony deposit represent the Annidale area, whereas the South (Central and East subzones), George Murphy, Richard, and Jubilee zones represent gold mineralized areas in the Clarence Stream region.To facilitate the geochemical investigation of the various deposits and occurrences, an Olympus Vanta™ portable X-ray fluorescence spectrometer (pXRF) was used to rapidly analyse the composition of the different auriferous quartz (-carbonate) veins and characterize the alteration assemblages related to gold mineralization. The precision and accuracy of the pXRF data was monitored through QA/QC procedures, with the resulting corrected pXRF data undergoing principal component analysis (PCA) to fully interrogate the large data set.The PCA results highlight hydrothermal alteration and mineralization geochemical trends in the studied orogenic and intrusion-related gold deposits and occurrences. Some gold pathfinder elements reflect these different trends on the PC analysis on the studied samples. From the different PCs, various information about alteration and mineralization can be deduced. In Annidale area PC1 retrieves positive loadings of S, Cu, As, Pb, Zn, Fe, and Sb consistent with mineralization, PC2 displays positive loadings of Ca, Sr, Y, Mn and Ti, and PC3 extracts information about K, Rb, Ba, Zr, and Al consistent with alteration. In the Clarence Stream area, PC1 retrieved information about Al, K, Zr, Ba, Nb, Th and Rb consistent with alteration, PC2 displays positive loadings of As, Sb, Fe, Co, and S consistent with mineralization and PC3 extracts information about Zn, Pb, Mn, Fe, Cu, S and Si.Data obtained from the micro-X-Ray fluorescence–energy dispersive spectrometer (μ-XRF) analyses of the same sample suite concur with the alteration and mineralization characteristics identified using pXRF; these data indicate that chloritic and sericitic alteration with sulphides are associated with quartz (-carbonate) veins. The μ-XRF analysis is also helpful to further investigate sulphide and gold mineralization, as well as to locate potentially datable minerals, such as titanite, rutile, zircon, apatite, and monazite, in the gold-bearing quartz (-carbonate) veins; these data identified rutile and titanite in the Annidale samples and apatite in Clarence Stream samples that are being followed up geochronologically.

Telluride Mineralogy of the Deer Horn Au-Ag-Te-(Bi-Pb-W) Deposit, British Columbia: Implications for the Generation of Tellurides

ABSTRACTThe Deer Horn deposit, located 150 km south of Smithers in west-central British Columbia, is an Eocene polymetallic system enriched in Au-Ag-Te with lesser amounts of Bi-Pb-W; the Au and Ag are hosted in Te-bearing minerals and Ag-rich gold (Au-Ag alloy). A quartz-sulfide vein system containing the main zones of Au-Ag-Te mineralization and attendant sericite alteration occurs in the hanging wall of a local, spatially related thrust fault and is genetically related to the nearby Eocene Nanika granodiorite intrusive suite. Tellurium-bearing minerals commonly form isolated euhedral to subhedral grains or composite grains (up to 525 μm in size) of Ag-, Bi-, Pb-, and Au-rich tellurium-bearing minerals (e.g., hessite, tellurobismuthite, volynskite, altaite, and petzite). Panchromatic cathodoluminescence imaging revealed four generations of quartz. Within remnant cores of quartz I, local oscillatory zoning occurs in quartz II. Fine-grained veinlets of quartz III and IV crosscut quartz I and II, showing evidence of at least two deformation events; late-forming veinlets of calcite crosscut all generations of quartz. The tellurides and Ag-rich gold occur in stage III quartz. Three types of fluid inclusions were observed in stage III and IV quartz: (1) aqueous liquid and vapor inclusions (L-V); (2) aqueous carbonic inclusions (L-L-V); and (3) carbonic inclusions (vapor-rich). Primary fluid inclusions related to the telluride mineralization within quartz III were tested with microthermometry, along with a few primary inclusions from quartz IV. Homogenization temperatures are 130.0–240.5 °C for L-V inclusions and 268.0–336.4 °C for L-L-V inclusions. Aqueous carbonic inclusions had solid CO2 melting temperatures from –62.1 to –56.8 °C, indicating the presence of ≈1 to 30 mol.% dissolved methane in these inclusions.The Deer Horn Au-Ag-Te-(Bi-Pb-W) deposit is a reduced intrusion-related gold system characterized by sheeted veins, metal zoning, low salinity aqueous-carbonic fluids, and a genetic relationship to an Eocene granodiorite. Values of δ34S of pyrite vary from –1.6 to 1.6 per mil and are compatible with a magmatic source of sulfur.

Rare and Critical Metals in Pyrite, Chalcopyrite, Magnetite, and Titanite from the Vathi Porphyry Cu-Au±Mo Deposit, Northern Greece

The Vathi porphyry Cu-Au±Mo deposit is located in the Kilkis ore district, northern Greece. Hydrothermally altered and mineralized samples of latite and quartz monzonite are enriched with numerous rare and critical metals. The present study focuses on the bulk geochemistry and the mineral chemistry of pyrite, chalcopyrite, magnetite, and titanite. Pyrite and chalcopyrite are the most abundant ore minerals at Vathi and are related to potassic, propylitic, and sericitic hydrothermal alterations (A- and D-veins), as well as to the late-stage epithermal overprint (E-veins). Magnetite and titanite are found mainly in M-type veins and as disseminations in the potassic-calcic alteration of quartz monzonite. Disseminated magnetite is also present in the potassic alteration in latite, which is overprinted by sericitic alteration. Scanning electron microscopy and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of pyrite and chalcopyrite reveal the presence of pyrrhotite, galena, and Bi-telluride inclusions in pyrite and enrichments of Ag, Co, Sb, Se, and Ti. Chalcopyrite hosts bornite, sphalerite, galena, and Bi-sulfosalt inclusions and is enriched with Ag, In, and Ti. Inclusions of wittichenite, tetradymite, and cuprobismutite reflect enrichments of Te and Bi in the mineralizing fluids. Native gold is related to A- and D-type veins and is found as nano-inclusions in pyrite. Titanite inclusions characterize magnetite, whereas titanite is a major host of Ce, Gd, La, Nd, Sm, Th, and W.

The Alteration and Mineralization Characteristics of Miocene Porphyry Cu-Au Deposits of Chagai Magmatic Belt, District Chagai, Balochistan, Pakistan

Subduction related Miocene porphyry type deposits are found in the east-west trending Chagai magmatic belt (CMB) in Pakistan's western margin, Balochistan. This arc exists on the west segment of the Tethyan metallogenic belt in the south-west of Pakistan. Tethyan metallogenic belt is widely spread over 12,000 km from east to west direction from Indochina, Tibet, Pakistan, Iran, Turkey and Alpine mountain range in Europe. During the last thirty to forty years several porphyry deposits have been reported in the Chagai magmatic arc, including the very large Reko Diq H14-H15, large Saindak, Tanjeel, H35, H8 and medium Dasht-e-Kain porphyry deposits and many small porphyry copper deposits. These porphyry deposits were developed within the phase of calc-alkaline type magmatism in the Chagai arc. Tonalite, quartz diorite, and monzonite host the porphyry deposits within the adjacent sedimentary wall rock units of Sinjrani Volcanic Group, Juzzak, Saindak, and Amalaf Formations. The concentric zonal pattern of hydrothermal alteration in these porphyry deposits of the Chagai magmatic arc follows the world's major porphyry deposits' alteration pattern. Zones of hydrothermal alteration from distal to proximal part includesa potassic alteration, sericitic-clay-chlorite alteration, sericitic alteration, argillic alteration and propylitic alteration. Major ore mineralization in these deposits is of copper, gold, silver, molybdenum, and minor constituents of other base metals that have been reported to occur within hydrothermal alteration zones in the Miocene porphyry Chagai magmatic arc

Occurrence and remobilization of gold in the Dayingezhuang deposit in Jiaodong, North China Craton: Evidence from textural and geochemical features of pyrite

The Dayingezhuang gold deposit in the Jiaodong district, eastern margin of the North China Craton is hosted in Mesozoic granitic rocks and consists of quartz-sulfide veins/veinlets and sulfide disseminations in alteration envelopes. Previous studies mainly focused on the geochronology, sources of ore-forming fluids and metals to investigate the ore genesis. However, enrichment mechanism of Au and other associated trace metals remain unclear. In this study, we present detailed textures and in-situ LA-ICP-MS trace-element compositions of different generations of pyrite, as well as EMP analysis of Au-bearing minerals to discuss the occurrence and enrichment mechanism of Au at this deposit.Three generations of pyrite (Py1, Py2 and Py3) formed during three hydrothermal ore stages (I, II, and III) at Dayingezhuang. Py1 occurs as disseminations in sericitic alteration assemblages and is characterized by low Au (mean 0.15 ppm), Ag, As and Te contents. The time-resolved depth-concentration profiles indicate that Au in Py1 mainly occurs as nanoparticles and/or micron-sized inclusions. Py2 can be further divided into the early undeformed Py2a and later Py2b, which is the product of deformed Py2a with different degrees of brittle to plastic deformation and recrystallization. Py2a in pyrite-siderite-quartz veins is relatively enriched in invisible Au (mean 0.41 ppm), Ag, As, and Te compared to Py1, and contains numerous micron-sized Au inclusions. In contrast, Py2b contains lesser invisible Au (0.21 ppm) and host abundant gold minerals along the grain boundaries and microfractures. Py3 in polymetallic sulfide veins has little Au. As a whole, Au in pyrite is positively correlated with Ag and Te, which is consistent with the results of EMP analysis showing the occurrence of Au as electrum, native gold and minor petzite in pyrite. Such evidences show that the deformation and recrystallization of auriferous Py2a potentially caused local remobilization of Au (mainly as micron-sized inclusion Au) via solid-state ductile flow and subsequent reconcentration of Au in microfractures of Py2b. The pyrite deformation and Au remobilization events were suggested to be related to the continuous reactivation of the regional Zhaoping Fault contemporaneous with gold mineralization. Our study highlights the importance of remobilization and reconcentration of Au triggered by syn-ore tectonic activities at Dayingezhuang and possibly other Au deposits in the Jiaodong district.

Identification of clays and Fe oxide minerals rich alteration zones using a Landsat 8 image of Pu Sam Cap area, Lai Chau

The hydrothermal alteration zones are the important sign for mineral exploration and can be identified by remote sensing images completely, but this is limited due to the effect of vegetable. We address this problem by a method called “Directed Principal Component Analysis” (DPCA) that involves calculating principal components on two input band ratio images. One ratio is a geological discriminant, confused by the presence of vegetation; the second ratio is chosen for its suitability as a vegetation index. DPCA applied on Landsat 8 image in Pu Sam Cap area, Lai Châu characteristied by argilic alteration, sericite alteration, etc., with the typical minerals like kaolinite, illite, etc., and pyrite, chalcopyrite, magnetite; specularite, etc., The results have identified Fe - rich zones in Bai Bang and Nam Tra areas; clay minerals are concentrated mainly in Nam Tra area and along the main faults. The results are also compared with previous research data and fieldtrip data that shows similarity and feasibility. This paper indicated limitation of Landsat image such as spatial resolution, spectral resolution, etc., when applied in the tropical area.

Genesis of the Yanghuidongzi Cu deposit, NE China: Constraints from H-O-Pb isotopic compositions and geochronological study

• The Yanghuidongzi Cu deposit classified as a porphyry type Cu deposit. • H-O isotopes indicate a mixing of magmatic water and meteoric water for ore fluids. • Pb-Re isotopes indicated a deep seated magma mixed with crustal materials for ore metals. • The Yanghuidongzi Cu deposit formed during Early Jurassic . The newly-discovered Yanghuidongzi porphyry Cu deposit is located in the southeastern part of Heilongjiang Province in NE China and represents one of the rare Jurassic porphyry Cu deposits within the easternmost segment of the Central Asian Orogenic Belt (CAOB). The Cu mineralization occurs as veins and disseminations hosted by granodiorite porphyry, associated with typical porphyry copper deposit alteration zoning, which is characterized by from an inner K-silicate zone through to a quartz–sericite zone to an outer propylitic zone, the K-silicate alteration and quartz–sericite alteration are closely related to mineralization. LA-ICP-MS zircon U-Pb data, sericite Ar-Ar and Molybdenite Re-Os data, and H-O and Pb isotopic compositions are used to constrain the ore-forming age and genesis of the Yanghuidongzi Cu deposit. LA-ICP-MS U-Pb dating of zircons from three granodiorite porphyry samples yielded weighted mean 206 Pb/ 238 U ages of 194.3 ± 1.2 Ma, 192.0 ± 2.0 Ma, and 194.6 ± 2.1 Ma respectively, whereas zircon U-Pb age of granodiorite in the study area yielded weighted mean 206 Pb/ 238 U age of 199.5 ± 1.5 Ma that are interpreted to be the emplacement age of these intrusions. 40 Ar- 39 Ar dating of sericite from a quartz-pyrite vein and a quartz-polymetallic sulfide vein yielded plateau ages of 193.9 ± 2.1 Ma and 193.6 ± 1.9 Ma, respectively, whereas five molybdenite samples yielded a Re-Os isochron age of 194.8 ± 2.1 Ma, with a weighted mean model age of 193.6 ± 1.2 Ma. Mineralization ages are consistent with the emplaced ages of the granodiorite porphyry within the analytical uncertainties, indicating that the Cu mineralization is genetically related to the granodiorite porphyry. The fluid δ 18 O fluid and δ 18 D fluid values range from −4.22‰ to 6.5‰ and from −92.8‰ to −65.7‰, respectively, indicating that the ore fluids were mixtures of magmatic and meteoric water. The 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 208 Pb/ 204 Pb values of the pyrite and chalcopyrite are 17.547–18.327, 15.446–15.505, and 37.408–38.113, respectively, suggesting a common, magmatic source for the sulfur. Taking Re (6.75–29.53 ppm) data into consideration, the sources of ore-forming materials may be from a mixture of crustal and mantle sources. Combining our new data with the Jurassic regional tectonic setting, the Yanghuidongzi Cu deposit and the related granitoids formed in a compressional tectonic setting are associated with the subduction of the Paleo-Pacific Plate beneath the Eurasian continent.

Evolution of Pyrite Compositions at the Sizhuang Gold Deposit, Jiaodong Peninsula, Eastern China: Implications for the Genesis of Jiaodong-Type Orogenic Gold Mineralization

Gold deposits in the Jiaodong Peninsula represent a primary gold resource in China and mostly exhibit similar ore-forming features related to sericite-quartz-pyrite alteration and other controls from (micro-)structural deformation. This study investigates the pyrite textures and trace elements in the Sizhuang gold deposit (&gt;100 t Au) to document the key factors impacting on the genesis of the Jiaodong-type orogenic deposits. Three main types of pyrite are identified: (1) the first generation of pyrite (Py1) occurs as disseminated euhedral to subhedral grains in K-feldspar-albite-rutile-hematite and sericite alteration (stage 1), (2) Py2 as aggregates in quartz-sericite-pyrite altered rocks or quartz-pyrite veins (stage 2) can be subdivided into Py2a as irregular cores, Py2b as a zoned overgrowth on Py2a, and Py2c as overgrowth on early pyrite, and (3) Py3 as fine-grained crystals in siderite-polymetallic veins (stage 3). Primary gold at the Sizhuang deposit is coevally or slightly later deposited with Py2b, Py2c, and Py3. Laser ablation–inductively coupled plasma mass spectrometry (LA–ICP–MS) analyses show that the highest Co and Ni contents in Py1 and high but variable Co in Py2b favors the involvement of deep high-temperature magmatic waters at stage 1 and middle stage 2. The elevated As contents from Py2a to Py2c and depletion of trace elements (e.g., Co, Ni, As and Te) and high Au/Co, Cu/Ni, and As/Ni values in Py2a and Py3, combined with published H-O isotope data, imply a meteoric water ingress during stage 2–3. Thus, the fluid evolution at Sizhuang is a consequence of pulsed deep magmatic fluid release plus progressive meteoric fluid ingress. The rhythmic Co–As–Ni–Au bands of Py2b additionally suggest episodic changes in the composition of ore-forming fluids. Moreover, the sharp textural features (e.g., pyrite overgrowth on previously cataclastic crystals) of Py2 and As-Cu-rich and Co-poor bands in zoned Py2b probably also reflect rapid metal deposition and self-organization and subsequent mineral crystal growth due to the pressure release during phase separation in the Sizhuang deposit. Considering the significantly concentrated gold (&gt;1300 t) in the regional Jiaojia fault zone and Au-bearing mineral formation related to phase separation (boiling) in the Sizhuang deposit, gold mineralization in the Sizhuang deposit was interpreted to be controlled by the pressure-driver owing to the seismic activities in the Jiaojia fault system.

Evolution of the Magmatic-Hydrothermal System at the Santa Rita Porphyry Cu Deposit, New Mexico, USA: Importance of Intermediate-Density Fluids in Ore Formation

Abstract The Santa Rita porphyry Cu deposit in New Mexico, USA, is characterized by a stockwork of three vein types that differ in morphology, mineralogy, and associated alteration assemblages. Early quartz veins associated with potassic alteration are composed of recrystallized granular quartz grains that host ubiquitous hypersaline liquid and vapor-rich fluid inclusions. The early quartz likely formed at high (≳500°C) temperatures and lithostatic pressures. Hypogene Cu mineralization at Santa Rita is in sulfide veins that reopened or crosscut the early quartz veins. The sulfide veins are surrounded by alteration halos containing chlorite and K-feldspar. Rare quartz crystals are present in some of these chalcopyrite and pyrite veins. The cores of the quartz crystals contain hypersaline liquid and vapor-rich fluid inclusions, whereas the rims mostly contain hypersaline liquid inclusions. The quartz crystals are interpreted to have formed close to the ductile-brittle transition as a result of the pressure drop from lithostatic to hydrostatic conditions. Formation of the quartz crystals was postdated by the deposition of Cu sulfides. Grain boundaries between the quartz and the sulfide minerals are irregular in shape, with sulfide crosscutting growth zones in the quartz. The Cu sulfides are interpreted to have formed from intermediate-density fluids that form secondary fluid inclusion assemblages in all earlier-formed quartz types. Microthermometric investigations showed that these fluid inclusion assemblages homogenize at ~385° to 435°C by critical or near-critical behavior and have salinities of &amp;lt;10 wt % NaCl equiv. The precipitation of Cu sulfides occurred as a result of cooling of these fluids following their escape from the lithostatic into the hydrostatic realm. Retrograde quartz solubility caused the corrosion of earlier-formed quartz during Cu sulfide deposition. The youngest veins at Santa Rita are composed of quartz and pyrite. These veins are associated with intense sericite alteration that overprinted all earlier alteration assemblages. The late quartz hosts primary and secondary liquid-rich fluid inclusions, but no intermediate-density fluid inclusions were identified. This quartz vein type formed at temperatures &amp;lt;360°C and hydrostatic pressures. The paragenetic relationships show that hypogene Cu mineralization at Santa Rita postdated potassic alteration of the host rocks. The Cu mineralization was formed by cooling intermediate-density fluids with critical or near-critical densities as they escaped from lithostatic to hydrostatic conditions.

The role of porphyry-related skarns in the Chating porphyry copper and gold deposit, eastern China

The Chating deposit is a porphyry copper deposit in the Middle Lower Yangtze River Valley Metallogenic Belt, with skarns found in both the carbonate wall rock and in carbonate xenoliths in the intrusions. Detailed drill hole logging identified endoskarn and exoskarn in Chating, mainly distributed inside the ore–bearing quartz diorite porphyry instead of at the contact with the country rock. The skarns at Chating are unmineralized unless overprinted by porphyry related copper mineralization. Garnet in the Chating skarns can be divided into several types based on their occurrence and whether they were overprinted by porphyry mineralization. The garnets from the ore–bearing (G1a), barren endoskarn (G1b) and proximal ore–bearing exoskarn (G2a) are LREE-enriched, HREE–depleted with positive Eu anomalies whereas garnets from the barren massive exoskarn (G2b) are LREE-enriched with flat HREE and negative Eu anomalies. The G3 garnets are from marbleized skarn distal to the ore-bearing quartz diorite porphyry and consist of Al-rich and Fe-rich andradite; the Al–rich G3 garnets are LREE-depleted and HREE-enriched whereas the Fe-rich G3 garnets are LREE-enriched and HREE-depleted, both have negative Eu anomalies. The physicochemical conditions and composition of skarn-forming fluids controlled the REE, Eu, U and Y distribution in the garnets. The similarities of the REE patterns to those of magmatic–derived fluids suggests a dominantly magmatic fluid formed the endoskarn and proximal exoskarn. Fluid–rock interaction and addition of external fluids diluted the fluid that formed the exoskarn, decreasing the Cl and metal contents, resulting in lower REE contents and negative Eu anomalies in G2b and G3 garnets. The δ34S data for anhydrite from potassic alteration, sericite alteration, endoskarn and exoskarn range from 3.51‰ to 10.92‰, consistent with a dominantly magmatic fluid source. The δ34S for the anhydrite from the skarns ranges from 3.51‰ to 8.74‰, which combined with the absence of coeval sulfides, suggests a very high oxygen fugacity for the skarn-forming fluids. The small-scale skarns in Chating contain more anhydrite than garnet and consequently did not act as ground preparation as they do in typical skarn deposits. We propose that the anhydrite-rich exoskarn and the small scale of the endoskarn, combined with the high oxygen fugacity and low Cl content in the skarn-forming fluids resulted in the barren skarns of the Chating deposit.

Pegmatite mapping using spectroradiometry and ASTER data (Zenaga, Central Anti-Atlas, Morocco)

The region of Angarf, located in the southern part of the Zenaga inlier (Central Anti-Atlas, Morocco), is known by the abundance of pegmatite veins, essentially constituted by quartz, muscovite and feldspar. These veins are hosted in the mica schists and granites of the Paleoproterozoic basement. Mapping of pegmatites was approached by using synergetic field data, spectroradiometric measurements, and ASTER data.Analysis and interpretation of the spectroradiometric data allowed the identification of an important sericitic alteration. The measured spectra of the pegmatites detected the presence of absorption bands at wavelengths of 900 nm, 1400 nm, 1900 nm, 2200 nm, 2350 nm, and 2450 nm, which allowed the selection of the most informative ASTER spectral bands for pegmatite mapping. After geometric, radiometric, and atmospheric corrections to ASTER data, some processing techniques were applied, including Principal Component Analysis (PCA), Minimum Noise Fraction (MNF), and Band Ratios (BR). Then, several RGB compound displays were analyzed using the results of these treatments. Three combinations of RGB were selected because of their potentials to extract the pegmatites outcrops. The first RGB combines the PC2, PC1, and PC3, it's suited to achieve good separation between geological facies allowing the identification of pegmatites. The second considers the MNF2, PC1, and 6/3; it has the same mapping potential as PC combination. The third combines 1/3, 1/4, and 2/5, it has allowed the identification of more pegmatites found in the field compared to the other two combinations. This last combination proved to be the most suitable for simply and rapidly identifying pegmatites. This result was validated using field and spectroradiometric data.The approach presented in this study gave satisfactory results in comparison with field data. It is a low-cost technique that highly applicable for pegmatite mapping and in the exploration of their minerals. The result could assist the development of pegmatite exploration in the other regions.