Advanced Argillic Alteration Zones Research Articles

Alteration mineralogy, characteristics and shortwave infrared spectroscopy of white mica in the Zijinshan ore field, Fujian Province: Implications for porphyry Cu prospecting

The Zijinshan ore field is situated in the southeastern part of China. in which contains the large Zijinshan high-sulfidation Cu-Au deposit, the Luoboling porphyry Cu-Mo deposit, the Yueyang low-sulfidation Au-Ag deposit, the Longjiangting and the Wuziqilong tansitional Cu deposit, and the Xi’nan porphyry Cu-Mo prospect. Debates on genetic relationship among these deposits, especially the relationship between the Zijinshan Cu-Au deposit and the adjacent Luoboling deposit is a question of importance for further exploration in this ore field. In this contribution, the alteration mineralogy, alteration texture, zonation and mineral chemistry, in combination with shortwave infrared spectroscopy (SWIR) analysis of white mica were used to help focus exploration and assessment of hydrothermal deposits in the Zijinshan ore field.In this study, diaspore-pyrophyllite alteration zone, chlorite-sericite alteration zone and propylitic alteration zone were first identified in the deep drill core of the Zijinshan Cu-Au deposit, which gives way upward to quartz-alunite-kaolinite zone, quartz-alunite zone and the silicic alteration zone. In the Xi’nan Cu-Mo prospect, diaspore-pyrophyllite alteration zone was first recognized in the shallow level with the chlorite-sericite alteration zone and propylitic alteration zone in the deeper level. Andalusite- sericite ± diaspore alteration zone was first recognized in the upper part of the Luoboling Cu-Mo deposit and the deeper part of the Wuziqilong Cu deposit. It indicates that a pervasive occurrence of diaspore -pyrophyllite ± andalusite alteration zones in the Zijinshan ore field, which may potentially represent a transitional environment between the top of porphyry alteration zones and the base of advanced argillic alteration zones. Minerals of the white mica group are extensively distributed in various alteration zones of the Zijinshan ore field. The SWIR analysis of white mica indicated that the wavelength position of the Al-OH (∼2,200 nm; wAlOH) absorption feature increases gradually from the shallow kaolinite-dickite alteration zone to the deep potassic alteration zone. In the advanced argillic alteration zones, the range of wAlOH values of white mica is less than 2205 nm. Conversely, in the porphyry alteration zones, it always exceeds 2205 nm. It is evident that the andalusite-sericite alteration zone with higher wAlOH values (average of 2203 nm) is always proximal to the porphyry mineralization, which may act as indicators for deep porphyry prospecting. The results of electron probe microanalysis (EPMA) reveal that the early enrichment of Mg and depletion of Fe in white mica can be attributed to the preferential incorporation of Fe into iron oxides and iron sulfides in the potassic and propylitic alteration zones. Overall, there is a negative correlation between wAlOH and Al, while wAlOH exhibits a positive correlation with the sum of Fe + Mg + Mn. The distribution characteristics of alteration zones and the variation patterns of the wAlOH of white mica indicate that there are probably several paleo-thermal centers in the deep parts of the Zijinshan ore field, located respectively in the deep parts of the Xi’nan Cu-Mo prospect and the deep part of the Zijinshan Cu-Au deposit and the deep parts of the Wuziqilong Cu deposit, and the latest seems to be more fertile and deserves further exploration.

The impact of livestock activities and geochemical processes on groundwater quality of fractured volcanic rock aquifer: Lake Çıldır watershed (NE Turkey)

This paper presents the impact of livestock activities and geochemical processes on the water quality of a fractured volcanic rock aquifer in the Lake Çıldır watershed, located at the northeastern part of Turkey. The existence of a high livestock population and animal grazing activities in meadow and pasturelands of the watershed during the short summer period poses serious stress on both surface and groundwater resources being the only drinking water supply for the local communities. Therefore, understanding the effect of grazing and livestock breeding activities occurring in the recharge areas of the fractured volcanic rock aquifer is vital to take precautions in order to protect limited water supplies at the watershed and vulnerable lake ecosystem as well. The mean nitrate content of the groundwater was measured at 6.4 ± 6.6 (std. dev) mg/L in the wet (before grazing) period and 7.1 ± 5.9mg/L in the dry (after grazing) period. Despite low nitrate concentration levels of groundwater, microbial contamination was observed in the spring waters at alarming levels especially after the animal grazing activities. 56%, 26%, and 11% of the groundwater samples showed bacterial contamination in terms of total coliform, fecal coliform, and fecal streptococci contents, respectively, prior to grazing activity, while in pursuit of intense livestock grazing at highland, these microbial indicators have been increased to 92%, 85%, and 77% in the dry period. A significant increase observed in fecal contamination indicates the negative impact of livestock activities on groundwater quality. Al (200-638µg/L) and Fe (66-218µg/L) enrichments locally observed in groundwater were related to advanced argillic alteration (kaolinization) and hematization zones in pyroclastic rocks.

Sulphide geochemistry of the superlarge Tiegelongnan Cu (Au) deposit in Tibet, China: Implication for the mineralization process

The Tiegelongnan deposit in central Tibet presents a typical high‐sulfidation porphyry Cu (Au) mineralization system. Optical microscopy, scanning electron microscopy–energy dispersive spectrometry (SEM–EDS), and laser ablation inductively coupled plasma mass spectrometry (LA–ICPMS) were used to understand the mineralization processes. The advanced argillic alteration zone directly contacts the phyllic alteration zone, which is linked to the Early Cretaceous porphyritic intrusions. In this study, the spatial distributions of chief copper sulphides with variable gangue minerals are illustrated. The deep inner phyllic zone typically produced an end‐member assemblage of chalcopyrite–sericite (±dolomite), which trended upwards to produce more bornite–sericite (±siderite ± magnesite), and subsequently, the advanced argillic alteration yielded the representative end‐member assemblage of tennantite–alunite ± (aluminium‐phosphate‐sulphate, namely, APS, ±kaolinite). In the phyllic–advanced argillic transition zone, intensive covellite precipitation with the widespread occurrence of sericite–kaolinite (±APS) assemblage is proposed as an important feature in this study, which is mainly produced on the southwest side of the ore‐body centre. The typical co‐occurrence of chalcopyrite with dolomite at great depths indicates that it was related to a gently acidic fluid containing CO2; however, the pervasive tennantite–alunite association present at shallower levels suggests that fluids with SO2 were mainly involved and produced stronger acidic conditions. Acidic fluids are demonstrated to highly accelerate water‐rock alteration. Trace element analyses of the copper sulphides reflect that Au concentrations of bornite and tennantite are higher than chalcopyrite and covellite and present small signal variations. Moreover, comparing the presence of micron‐sized Au‐telluride in tennantite under advanced argillic alteration with the nano‐sized native gold in bornite resulting from phyllic alteration suggests that to a certain extent, Au enrichment is affected by the shift of more Te contents in fluid towards shallower levels, which could promote Au precipitation. Additionally, the Se contents of the selected samples were typically concentrated in chalcopyrite, bornite, and covellite, which yielded contents an order of magnitude greater than those in tennantite, indicating the intimate hydrothermal origin of the first three sulphides. Overall, the sulphide–gangue mineral associations and their copper sulphide geochemistry indicate that the hypogene–chalcopyrite of low Au contents from the phyllic zone closely corresponds to the action of gentle acidic fluids with CO2, while more acidic fluids with SO2 are involved in the formation of supergene tennantite with relatively high values of Au and Te in the advanced argillic alteration.

Mineralogy, hydrothermal alteration, fluid inclusion, and O–H stable isotopes of the Siah Jangal-Sar Kahno epithermal gold deposit, SE Iran

Siah Jangal-Sar Kahno deposit is located in the northern part of Taftan volcano in the Sistan and Balouchestan provinces, southeast of Iran, and is an example of a vein-type epithermal gold system with related stockwork and shear zone mineralization. The veins are hosted by flysch facies rocks of the Makran zone and subvolcanic dioritic porphyry. The NE-SW fault systems played an essential role in the genesis of alteration and mineralization in the area. Diorite porphyry ranges from alkali (Na2O + K2O) content of 4.1–6.66 wt%, and plot in the calc-alkaline to high-K calc-alkaline fields. The chondrite-normalized REE patterns for least altered porphyry diorite rocks, altered host rocks, and silica-carbonate vein show a LREE/HREE ratios of 10.40, 4.03, 4.00, and 2.66, respectively. Positive Eu anomalies in the silica-carbonate veins indicate the Ca-bearing minerals, such as plagioclase decomposition causing release of Eu into hydrothermal fluid and subsequent precipitation in silica-carbonate veins. Mineralization consist of quartz, adularia, calcite, pyrite, arsenopyrite, marcasite, Fe-poor sphalerite, galena, chalcopyrite, and native gold. Later supergene mineral assemblages consists of Fe-oxide and hydroxides, covellite, cerussite, and scorodite. Hydrothermal alteration is generally well developed enveloping the ore-bearing hydrothermal breccia and subdivided into prograde inner quartz-chlorite-pyrite-muscovite, and outer argillic alteration zones, with a regional barren, widespread near-surface supergene (blanket) advanced argillic alteration zone. Chemical discrimination by means of cationic R1-R2 diagram indicates that R1 increases, whereas R2 decreases with increasing argillic alteration. Microthermometry of fluid inclusions in quartz crystals from silica-carbonate vein show the homogenization temperatures (Thv-l) of 167°–332 °C with salinities in the range of 0.21–4.24 wt% NaCl eq. The O and H isotopic compositions of quartz from hydrothermal vein and argillic alteration simply show a low sulfidation epithermal environment with meteoric waters as the main fluid. Due to a narrow range in salinity of the fluids, very low sulfide diversity, sulfide volume, and presence of adularia suggest dominantly meteoric water in the deposit, supporting classification as a low-sulfidation epithermal system.

Geochemical, stable isotopic (S, O, H, C), microthermometric and geochronological (U-Pb) evidence on the genesis of the Pınarbaşı porphyry Cu-Mo mineralization (Gediz-Kütahya, Western Turkey)

The Pınarbaşı porphyry CuMo mineralization is located at northwest of Gediz (Kütahya-Turkey) and east of Simav (Kütahya-Turkey) in western Anatolia. The Pınarbaşı CuMo mineralization is hosted by Pınarbaşı granitoidic intrusion consisting of granite, granodiorite and quartz monzonite. Geochemical and geochronological evidences for Pınarbaşı granitoidic rocks show that they are high-K calc-alkaline, and I-type granitoid magma likely developed post-collisional extensional regime. The UPb zircon age of granite (18.88 ± 0.17 Ma) and quartz monzonite porphyry (18.27 ± 0.14) obtained from the Pınarbaşı granitoid show Early Miocene (Burdigalian). The Pınarbaşı CuMo mineralization predominantly comprises molybdenite, chalcopyrite, galena, sphalerite, pyrite, fahlore, magnetite, bornite, hematite, jarosite, malachite and orpiment occurred in disseminated form in veins/veinlets associated with potassic, phyllic (sericitic) and advanced argillic alteration zones. According to the paragenetic and crosscutting relationships of veins/veinlets, the ore-forming process were divided into three stages; early-stage: quartz – molybdenite ± K-feldspar ± pyrite veins associated with potassic alteration, middle-stage: quartz ± calcite ± chalcopyrite ± galena ± sphalerite ± molybdenite + pyrite veins in phyllic alteration and late-stage: quartz ± calcite ± pyrite veins associated with advanced argillic alteration. Three types of fluid inclusions in quartz distinguished were designated as L-rich L + V phases (Type-I), salt-bearing L + V + S (Type-II), and V-rich L + V phases (Type-III). FIs of the early and middle stages are predominantly Type-II and Type-III inclusions, whereas the late-stage minerals commonly contain Type-I inclusions. Homogenization temperatures and salinities of FIs trapped in the early-stage quartz range from 481 to 590 °C and 13.19 to 61.1 wt% NaCl equivalent, respectively. FIs in quartz of the middle-stage yield homogenization temperatures (Th) of 310 to 460 °C, while halite dissolution temperatures are ranged from 264 to 430 °C, and salinities of 7.9 to 50.3 wt% NaCl eq. Homogenization temperatures and salinities of FIs in calcite of the middle-stage are range from 270 to 420 °C, 3.4 to 49.1 wt% NaCl eq. The late-stage homogenize at temperatures of 138 to 240 °C, and salinities of 0.9 to 6.5 wt% NaCl eq. The δ34SH2S values (0.6 to 4.5‰) of sulfides (molybdenite, chalcopyrite, pyrite and galena) and the δ18OSMOW (6.9 to 9.6‰) - δD (−71 to −86‰) values of molybdenite-bearing quartz from Pınarbaşı CuMo mineralization suggest a magmatic origin for the ore-forming fluids. The δ13CPDB (from −4.65‰ to 0.55‰) and δ18OSMOW (from 9.05‰ to 18.76‰) values of calcite which is one of the most common gangue minerals in Pınarbaşı mineralization show a high temperature influence and/or sedimentary contamination process to magmatic carbonate as well as continental carbonate. The S–O–H–C and UPb isotopic compositions indicate that the metallic elements and fluids came primarily from a magmatic source linked to Miocene intrusion. The geological, geochronological, and geochemical data support a magmatic-hydrothermal origin for the Pınarbaşı CuMo mineralization and confirm that mineralization is formed from an Early Miocene porphyry-related magmatic-hydrothermal system that is genetically linked with Eğrigöz and Pınarbaşı granitoids.

Comparison of Different Algorithms to Map Hydrothermal Alteration Zones Using ASTER Remote Sensing Data for Polymetallic Vein-Type Ore Exploration: Toroud–Chahshirin Magmatic Belt (TCMB), North Iran

Polymetallic vein-type ores are important sources of precious metal and a principal type of orebody for various base-metals. In this research, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) remote sensing data were used for mapping hydrothermal alteration zones associated with epithermal polymetallic vein-type mineralization in the Toroud–Chahshirin Magmatic Belt (TCMB), North of Iran. The TCMB is the largest known goldfield and base metals province in the central-north of Iran. Propylitic, phyllic, argillic, and advanced argillic alteration and silicification zones are typically associated with Au-Cu, Ag, and/or Pb-Zn mineralization in the TCMB. Specialized image processing techniques, namely Selective Principal Component Analysis (SPCA), Band Ratio Matrix Transformation (BRMT), Spectral Angle Mapper (SAM) and Mixture Tuned Matched Filtering (MTMF) were implemented and compared to map hydrothermal alteration minerals at the pixel and sub-pixel levels. Subtle differences between altered and non-altered rocks and hydrothermal alteration mineral assemblages were detected and mapped in the study area. The SPCA and BRMT spectral transformation algorithms discriminated the propylitic, phyllic, argillic and advanced argillic alteration and silicification zones as well as lithological units. The SAM and MTMF spectral mapping algorithms detected spectrally dominated mineral groups such as muscovite/montmorillonite/illite, hematite/jarosite, and chlorite/epidote/calcite mineral assemblages, systematically. Comprehensive fieldwork and laboratory analysis, including X-ray diffraction (XRD), petrographic study, and spectroscopy were conducted in the study area for verifying the remote sensing outputs. Results indicate several high potential zones of epithermal polymetallic vein-type mineralization in the northeastern and southwestern parts of the study area, which can be considered for future systematic exploration programs. The approach used in this research has great implications for the exploration of epithermal polymetallic vein-type mineralization in other base metals provinces in Iran and semi-arid regions around the world.

Application of WorldView-3 imagery and ASTER TIR data to map alteration minerals associated with the Rodalquilar gold deposits, southeast Spain

The Rodalquilar epithermal quartz-alunite gold deposits that occur within the Rodalquilar caldera complex in southeast Spain, are associated with a pronounced hydrothermal alteration of the country rocks. The hydrothermal alteration zones that are exposed on the surface consist of the vuggy silica zone, the advanced argillic alteration zone, the intermediate argillic alteration zone, the propylitic alteration zone, and a second stage supergene acid sulfate alteration. High spatial resolution multispectral imagery recorded by the WorldView-3 satellite was used in this study to map the spatial distribution of the main alteration minerals in the Rodalquilar caldera complex. Thermal infrared (TIR) data of the ASTER satellite were used to detect the quartz-rich zones. The analysis of the Rodalquilar WorldView-3 data was based on the Adaptive Coherence Estimator (ACE), a partial unmixing algorithm. The ACE processing accurately mapped the spatial distribution of alunite, kaolinite, illite and goethite. Alunite is abundant in the vuggy silica and advanced argillic alteration zones, and in the second stage supergene acid sulfate alteration. Kaolinite is predominant in the intermediate argillic alteration zone. Illite is abundant in the outer parts of the intermediate argillic alteration zone. Goethite image maps gossans that mainly occur in the vuggy silica and advanced argillic alteration zones, and in the areas characterized by the second stage supergene acid sulfate alteration. The detection of quartz-rich zones from the ASTER TIR data complemented the WorldView-3 mapping results. The study shows the efficiency of high spatial resolution multispectral remote sensing imagery recorded by the WorldView-3 satellite for district-level mineral exploration studies.

Supergene Mass-Balance Study Assuming Zero Lateral Copper Flux Using Geostatistics to Recognize Metal Source Zones in Exotic Copper Deposits

Recognition of effective factors that influence the spatial extension of supergene weathering zones is important both for the identification of high potential areas of exotic deposits and for the cost-effective planning of mining. In particular, recognition of exotic mineralization around porphyry copper deposits early in mine development prevents them from being buried beneath mine infrastructures such as waste dump and tailing structures. Mass-balance modeling, a practical method for determining high potential areas of undiscovered exotic mineralization, investigates important factors in forming exotic deposits. Mass-balance modeling is a two-phase methodology that becomes progressively more detailed. An initial result, presented here as phase 1, is based solely on Cu assays. Phase 2 incorporates relict sulfide mineral studies to improve phase 1 modeling results and computes actual fluxes of copper that escaped vertically downward from the leached cap to form the enrichment blanket and then flowed laterally away to form exotic mineralization. In addition, geostatistical approaches, especially sequential Gaussian simulation, are useful tools for investigating the spatial relationships and modeling of mass-balance results in phase 1 studies. This paper introduces a method for interpolation and downscaling of the preliminary mass-balance analysis (phase 1) to highlight the role of geological features in the evolution of the supergene process. Using only copper assays without any need for relict sulfide mineralogy, this approach can be used to approximately identify the geographic direction of metal movement in exotic copper deposits, and thus serve as an initial exploration guide in prospecting for exotic deposits. For this, a vertical columnar block model was constructed for each of the supergene weathering zones and preliminary analysis of mass balance was conducted to reconstruct the apparent total leached zone column height assuming zero lateral flux. This analysis was applied to each of the vertical block model columns. The results of mass balance were interpolated in a 5 × 5 m grid by sequential Gaussian simulation method, and the simulated surface of the total leached zone was conflated with geological features. The roles of topography, argillic alteration and linear structures were identified in the transport of supergene solutions in the Miduk porphyry copper deposit of Iran. In the northern section of the deposit, which is in accordance with the topography gradient and the presence of advanced argillic alteration zone, the computed top total of leaching is below the actual surface topography, whereas the hypogene isograd curves confirm the expansion of primary copper in these areas. The northern section of the deposit was introduced as a susceptible area for the removal of copper-bearing solutions from the supergene enrichment system.

Mineralization of the Northwest Quartz-Pyrite-Gold Veins: Implications for Multiple Mineralization Events at Lepanto, Mankayan Mineral District, Northern Luzon, Philippines

Abstract The Northwest quartz-pyrite-gold veins are situated 500 m east of the Lepanto fault in Mankayan, Luzon, Philippines. Most vein mineralization is hosted by the Lepanto metavolcanic basement rocks at an elevation between 700 and 1,050 m. The earliest stage, stage 1, is characterized by sphalerite + chalcopyrite + pyrite ± magnetite veins cutting the host rocks that were altered to chlorite + illite + epidote. Precious metal deposition started in stage 2 as electrum, native gold, and gold-silver tellurides deposited with pyrite, quartz, and carbonate. Deposition of gold and silver tellurides continued in stage 3a with abundant pyrite and tennantite-tetrahedrite solid solution intergrown with chalcopyrite, bornite, and minor sphalerite. The stage 3a veins and host-rock alteration are characterized by abundant muscovite and quartz, while the stage 3b veins and alteration consist of quartz, pyrophyllite, alunite, and dickite. Enargite and luzonite are the dominant sulfide minerals in stage 4, which are either disseminated in silicified host rock or within wide quartz veins. Lesser amounts of quartz and abundant pyrite with inclusions of enargite and luzonite were precipitated in stage 5. Microthermometry on fluid inclusions in quartz of stages 2, 3a, and 4 indicates boiling of the hydrothermal fluids. Bulk gas analysis on fluid inclusions in quartz shows that the stage 2 and 4 fluids had components derived from basaltic and andesitic magma, respectively. Fluids that formed stage 4 quartz were more diluted by meteoric water than the fluids that formed the stage 2 veins. Radiometric 40Ar/39Ar dating on alunite separated from the stage 3b advanced argillic alteration zone yielded 2.2 ± 0.1 Ma. Sulfur isotope compositions of the Northwest quartz-pyrite-gold deposit reveal a bulk δ34S of approximately 5‰, similar to the calculated value for the adjacent Far Southeast porphyry deposit. Calculated oxygen and hydrogen isotope ratios of the fluids of the Northwest quartz-pyrite-gold deposit stage 3b dickites are similar to those that formed the illite alteration in the Far Southeast porphyry deposit but are higher in δ18O when compared to the fluids that formed the kandites in the Lepanto enargite deposit. The northward cooling of mineralizing fluids previously reported in the Lepanto enargite deposit is not consistent with the mineralogic indications in the Northwest quartz-pyrite-gold deposit. These data indicate multiple mineralization events in the Mankayan district, which is one of the largest mineral districts in the western Pacific.

Mineralogical Study of the Advanced Argillic Alteration Zone at the Konos Hill Mo–Cu–Re–Au Porphyry Prospect, NE Greece

The Konos Hill prospect in NE Greece represents a telescoped Mo–Cu–Re–Au porphyry occurrence overprinted by deep-level high-sulfidation mineralization. Porphyry-style mineralization is exposed in the deeper parts of the system and comprises quartz stockwork veins hosted in subvolcanic intrusions of granodioritic composition. Ore minerals include pyrite, molybdenite, chalcopyrite, and rheniite. In the upper part of the system, intense hydrothermal alteration resulted in the formation of a silicified zone and the development of various advanced argillic alteration assemblages, which are spatially related to N–S, NNW–SSE, and E–W trending faults. More distal and downwards, advanced argillic alteration gradually evolves into phyllic assemblages dominated by quartz and sericite. Zunyite, along with various amounts of quartz, alunite, aluminum phosphate–sulfate minerals (APS), diaspore, kaolinite, and minor pyrophyllite, are the main minerals in the advanced argillic alteration. Mineral-chemical analyses reveal significant variance in the SiO2, F, and Cl content of zunyite. Alunite supergroup minerals display a wide compositional range corresponding to members of the alunite, beudantite, and plumbogummite subgroups. Diaspore displays an almost stoichiometric composition. Mineralization in the lithocap consists of pyrite, enargite, tetrahedrite/tennantite, and colusite. Bulk ore analyses of mineralized samples show a relative enrichment in elements such as Se, Mo, and Bi, which supports a genetic link between the studied lithocap and the underlying Konos Hill porphyry-style mineralization. The occurrence of advanced argillic alteration assemblages along the N–S, NNW–SSE, and E–W trending faults suggests that highly acidic hydrothermal fluids were ascending into the lithocap environment. Zunyite, along with diaspore, pyrophyllite, and Sr- and Rare Earth Elements-bearing APS minerals, mark the proximity of the hypogene advanced argillic alteration zone to the porphyry environment.

Hydrothermal Alteration in Porphyry Cu-Mo-Au Mineralizations of the Chagai Arc, Balochistan, Pakistan

Subduction-related east-west trending Chagai Arc located in the western part of Pakistan. This arc is the western extension of Tethyan Magmatic Belt which is about 5000 km long and extends from central Europe, Turkey, Iran, and Pakistan. During the last four decades, several porphyry copper settings were reported from the Chagai Arc. Seven more famous occurrences are selected for the present study owing to more detailed work carried out on them. From west to east these deposits include Saindak, Reko Diq (formerly known as Koh-e-Dalil), Humai, Missi, Durbanchah, Dasht-e-Kain and Ziarat Pir Sultan. Hydrothermal alterations in the porphyry copper setting of Chagai Arc are mostly associated with tonalite porphyry stocks, except Durbanchah and Humai prospects which are hosted in dacite porphyry stocks, whereas Missi Prospect occurs in a granodiorite batholith. The alteration is normally developed in a concentric zonal pattern as observed in the majority of the world deposits, except that absence of a regular argillic and peripheral zone. In most of the occurrences the potassium silicate alteration zone (K-alteration zone) occurs usually within the intrusive porphyry stock, but in Saindak and Reko Diq deposit, some of the adjacent wall-rock sediments, and in Durbanchah setting the microdioritic country rock, has also undergone the K-alteration. Quartz sericitic or phyllic alterations zones are developed in all the occurrences as continuous or discontinuous haloes around the K-alteration zone except in Durbanchah prospect. In Humai prospect an advanced argillic alteration zone is developed around the K-alteration zone. Propylitic alteration has also developed in almost all settings and generally encircles the quartz sericitic alteration. The oxide mineralization is generally represented by goethitic jarositic, hematitic limonites and malachite, with minor pitch limonite, chrysochola, neotocite, brochanthite and molybdite. Hypogene mineralization is represented by pyrite, chalcopyrite and minor bornite. A regular supergene sulfide enrichment is only reported from the Reko Dik deposit and represented by chalcosite and covellite in other deposits restricted incipient type supergene sulfide enrichment is encountered. In terms of ore reserves the Riko Dik deposit is on the top with 2,200 million tons of copper followed by Saindak with 412 million tons and Dasht-e-Kain 350 million tons. Grade wise Reko Diq Deposit is again on the top with 0.53% Cu, 0.01% Mo and 0.3g/t Au, followed by Saindak with 0.4% Cu, 0.015% Mo and 0.35 g/t Au. Dasht-e-Kain deposit contains 0.35% Cu and 0.015% Mo. Gold has not been reported from the Dasht-e-Kain deposit. From other deposits of the Chagai Arc ore reserves and grade are not reported so far.

40Ar/39Ar and Rb‐Sr Ages of the Tiegelongnan Porphyry Cu‐(Au) Deposit in the Bangong Co‐Nujiang Metallogenic Belt of Tibet, China: Implication for Generation of Super‐Large Deposit

AbstractThe Tiegelongnan deposit is a newly discovered super‐large porphyry‐epithermal Cu‐(Au) deposit in the western part of the Bangong Co‐Nujiang metallogenic belt, Tibet (China). Field geology and geochronology indicate that the porphyry mineralization was closely related to the Early Cretaceous intermediate‐felsic intrusions (ca. 123–120 Ma). Various epithermal ore and gangue mineral types were discovered in the middle‐shallow part of the orebody, indicating the presence of epithermal mineralization at Tiegelongnan. Potassic, propylitic, phyllic and advanced argillic alteration zones were identified. 40Ar/39Ar dating of hydrothermal biotite (potassic zone), sericite (phyllic zone), and alunite (advanced argillic zone) in/around the ore‐bearing granodiorite porphyry yielded 121.1±0.6 Ma (1σ), 120.8±0.7 Ma (1σ) and 117.9±1.6 Ma (1σ), respectively. Five hydrothermal mineralization stages were identified, of which the Stage IV pyrite was Rb‐Sr dated to be 117.5±1.8 Ma (2σ), representing the end of epithermal mineralization. Field geology and geochronology suggest that both the epithermal and porphyry mineralization belong to the same magmatic‐hydrothermal system. The Tiegelongnan super‐large Cu‐(Au) deposit may have undergone a prolonged magmatic‐hydrothermal evolution, with the major mineralization event occurring at ca.120–117Ma.

Identification of Multi-Style Hydrothermal Alteration Using Integrated Compositional and Topographic Remote Sensing Datasets

The western part of the island of Milos, Greece has undergone widespread, intense alteration associated with a range of mineralization, including seafloor Mn-Fe-Ba, sub seafloor Pb-Zn-Ag, and epithermal Au-Ag. The surrounding country rocks are a mixture of submarine and subaerial calc-alkaline volcanic rocks ranging from basaltic andesite to rhyolite in composition, but are predominantly andesites and dacites. The current surface spatial distribution of the alteration mineralogy is a function not only of the original hydrothermal, but also subsequent tectonic and erosional processes. The high relief and the excellent rock exposure provide ideal conditions to evaluate the potential of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite remote sensing data to identify and differentiate the different styles of alteration mineralisation. Laboratory spectral reflectance and calculated emittance measurements of field samples, supported by XRD analysis and field mapping, were used to support the analysis. Band ratio and spectral matching techniques were applied to the shortwave-infrared (SWIR) reflectance and thermal-infrared (TIR) emissivity imagery separately and were then integrated with topographic data. The band ratio and spectral matching approaches produced similar results in both the SWIR and TIR imagery. In the SWIR imagery, the advanced argillic, argillic and hydrous silica alteration zones were clearly identifiable, while in the TIR imagery, the silicic and advanced argillic alteration zones, along with the country rock, were differentiable. The integrated mineralogical–topographic datasets provided an enhanced understanding of the spatial and altitude distribution of the alteration zones when combined with conceptual models of their genesis, which provides a methodology for the differentiation of the multiple styles of alteration.

Mapping advanced argillic alteration zones with ASTER and Hyperion data in the Andes Mountains of Peru

This study evaluates Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Hyperion hyperspectral sensor datasets to detect advanced argillic minerals. The spectral signatures of some alteration clay minerals, such as dickite and alunite, have similar absorption features; thus separating them using multispectral satellite images is a complex challenge. However, Hyperion with its fine spectral bands has potential for good separability of features. The Spectral Angle Mapper algorithm was used in this study to map three advanced argillic alteration minerals (alunite, kaolinite, and dickite) in a known alteration zone in the Peruvian Andes. The results from ASTER and Hyperion were analyzed, compared, and validated using a Portable Infrared Mineral Analyzer field spectrometer. The alterations corresponding to kaolinite and alunite were detected with both ASTER and Hyperion (80% to 84% accuracy). However, the dickite mineral was identified only with Hyperion (82% accuracy).

Mineralogical study on volcanic ash of the eruption on September 27, 2014 at Ontake volcano, central Japan: correlation with porphyry copper systems

The volcanic ash of the eruption on September 27, 2014 at Ontake volcano consists mostly of altered rock fragments. The ash contains partly altered volcanic rock fragments consisting of primary igneous minerals (plagioclase, orthopyroxene, titanomagnetite, and feldspars) and volcanic glass accompanied by alteration minerals to some extents, and contains no juvenile fragments. These features indicate that the eruption was a non-juvenile hydrothermal eruption that was derived from the hydrothermal system developed under the crater. The major minerals derived from hydrothermal alteration zones are silica mineral, kaolin-group mineral, smectite, pyrophyllite, muscovite, alunite, anhydrite, gypsum, pyrite, K-feldspar, albite, and rutile. Minor chlorite, biotite, and garnet are accompanied. Five types of alteration mineral associations are identified from observations on individual ash particles: silica–pyrite, silica–pyrite ± alunite ± kaolin, silica–pyrophyllite–pyrite, silica–muscovite ± chlorite, and silica–K-feldspar ± albite ± garnet ± biotite. The associations indicate development of advanced argillic, sericite, and potassic alteration zones under the crater. Occurrence of anhydrite veinlet and the set of alteration zones indicate hydrothermal alteration zones similar to late-stage porphyry copper systems. Comparing the mineral associations with the geologic model of the late-stage porphyry copper systems, the source depths of mineral associations are estimated to range from near surface to >2 km. The depths of advanced argillic alteration, sericite, and potassic zones are 0 to ~2, ~1.5 to ~2, and >2 km, respectively.

Geology of metamorphic rocks deriving from paleohydrothermal systems in the Mesoproterozoic Serra do Itaberaba Group, São Paulo State, southeastern Brazil

ABSTRACTIn the central portion of the Ribeira fold belt, southeastern Brazil, the Mesoproterozoic volcanosedimentary Serra do Itaberaba Group was deposited in an ocean basin having normal mid-ocean ridge basalt type basalts that evolved to a back-arc environment. This succession was affected by two medium-grade regional metamorphic events and a third low-grade retrometamorphic event. This geological map covers an area of approximately 16 km2, between 23°16′41.824″ and 23°18′47.744″ latitudes S, and 46°20′57.056″ and 46°23′18.933″ longitudes W, as a scale of 1:5000. It encompasses the metamorphic products of tectonically deformed paleohydrothermal systems that developed in a back-arc environment, which are spatially and genetically linked to small metamorphosed andesitic-rhyolitic bodies. These systems were responsible for lixiviation of Ca and alkali in deeper parts, carbonatization in shallower parts, and a first large chloritic alteration zone (CZ1) that was crosscut by small chloritic (CZ2), silicification, and advanced argillic alteration zones. The metamorphic products of CZ1 are cummingtonite/anthophyllite rocks, whereas those related to CZ2 are Mg-rich chloritites. The metamorphic products of silicification and advanced argillic alteration zones are rocks composed of quartz ± specularite and of corundum, margarite, sericite, tourmaline, rutile, and Ca-plagioclase, respectively. Those associated with Ca and alkali depletions are garnet-hornblende amphibolites, whereas those related to carbonatization zones are composed of diopside, hornblende, tremolite/actinolite, carbonate, clinozoisite/epidote, plagioclase, and quartz. Cummingtonite/anthopyllite rocks and Mg-rich chloritites are similar to those associated with metamorphosed Kuroko-type volcanogenic massive sulfide deposits, whereas rocks composed of corundum, margarite, sericite, tourmaline, rutile, and Ca-plagioclase are genetically associated with oceanic high-sulfidation magmatic-hydrothermal gold mineralization.

Constraints on Hf and Zr mobility in high-sulfidation epithermal systems: formation of kosnarite, KZr2(PO4)3, in the Chaquicocha gold deposit, Yanacocha district, Peru

We report the first occurrence of Hf-rich kosnarite [K(Hf,Zr)2(PO4)3], space group R-3c, Z = 6, in the giant Chaquicocha high-sulfidation epithermal gold deposit in the Yanacocha mining district, Peru. Kosnarite crystals are small (<100 μm) and occur in 2–3-mm-thick veins that cut intensively silicified rocks. The paragenesis includes a first stage of As-free pyrite and quartz (plus gratonite and rutile), followed by trace metal-rich pyrite [(Fe,As,Pb,Au)S2] and secondary Fe sulfates. Kosnarite is associated with quartz and is clearly late within the paragenetic sequence. Electron microprobe analyses (EMPA) of kosnarite show relatively high concentrations of HfO2 and Rb2O (7.61 and 1.05 wt.%, respectively). The re-calculated chemical formulas of kosnarite vary from KΣ1.00(Zr1.93Na0.01Hf0.01Mn0.01)Σ1.96(P3.04O4)Σ3 to (K0.92Rb0.05Na0.03)Σ1.00(Zr1.81Hf0.19)Σ2.00 [(P2.98Si0.02As0.01)Σ3.01O4]Σ3, where Hf and Rb are most likely incorporated according to a coupled substitution of Hf4+ + Rb+ ⇔ Zr4+ + K+. Back-scattered electron (BSE) images and elemental mapping of kosnarite reveal that Hf and Rb are enriched in 2–10-μm-wide oscillatory and/or sector zones. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) observations of such zones reveal a pattern of alternating, 5–50-nm-thick, Hf-rich and Zr-rich nanozones. These high-resolution observations indicate that the incorporation of Hf does not appear to cause significant distortion in the kosnarite structure. Semiquantitative TEM-energy-dispersive X-ray spectrometry (EDS) analyses of the nano-layers show up to 22 wt.% of HfO2, which corresponds to 31 mol% of the hypothetical, KHf2(PO4)3, end-member. The presence of kosnarite in the advanced argillic alteration zone at Yanacocha is indicative of Hf and Zr mobility under highly acidic conditions and points towards an unforeseen role of phosphates as sinks of Zr and Hf in high-sulfidation epithermal environments. Finally, potentially new geochronological applications of highly insoluble vein kosnarite, including Rb-Sr dating, may provide further age constraints in pervasively altered areas where other isotopic systems might have been reset.

Evaluation of Earth Observing-1 (EO1) Data for Lithological and Hydrothermal Alteration Mapping: A Case Study from Urumieh-Dokhtar Volcanic Belt, SE Iran

This study evaluates the capability of Advanced Land Imager (ALI) and Hyperion Earth Observing-1 (EO1) data for lithological and hydrothermal alteration mapping. Several image processing methods were applied to ALI and Hyperion images covering the Meiduk and Sar Cheshmeh porphyry copper mining districts, SE Iran. Feature-oriented principal components selection, developed band ratio and minimum noise fraction methods were able to yield spectral information for enhancing the hydrothermally altered rocks and lithological units at regional scale using ALI data. Mixture-tuned matched-filtering method discriminated hydrothermal alteration areas from surrounding rock units using shortwave infrared bands of ALI. Analytical imaging and geophysics (AIG)-developed hyperspectral analysis processing methods were applied to the visible and near infrared and shortwave infrared bands of Hyperion for mapping iron oxide/hydroxide minerals and clay mineral assemblages at district scale. Supergene altered areas consisting of iron oxide/hydroxide minerals such as hematite, limonite, jarosite and goethite were detected using visible and near infrared bands of Hyperion. Phyllic, advanced argillic and propylitic alteration zones associated with porphyry copper mineralization were discriminated using shortwave infrared bands of Hyperion. The achievements of this investigation indicate considerable implications for geologists to use Earth Observing-1 data for porphyry copper and epithermal gold exploration.

Unveiling the hydrothermal mineralogy of the Chapi Chiara gold prospect, Peru, through reflectance spectroscopy, geochemical and petrographic data

Southern Peru contains important epithermal Au–Ag (±base metals) deposits, such as Canahuire, Tucari, Santa Rosa, Caylloma, Shila and Paula. The Chapi Chiara gold prospect is located in this region and is part of a paleo-stratovolcano of the Upper Miocene–Pliocene. The hydrothermal alteration of the prospect was characterized based on spectroradiometric data, geochemistry and petrography. The mineralogical data, interpreted based on reflectance spectroscopy, were spatialized using the sequential indicator simulation technique for producing probabilistic maps of alteration. The inner part of the paleo-stratovolcano (SW sector) is marked by three main cores of advanced argillic alteration (AAA) (quartz–alunite supergroup minerals–kaolinite–dickite±topaz±pyrophyllite±diaspore) associated with topographic highs. The AAA1 core is surrounded by argillic alteration (quartz–illite–paragonitic illite–smectite±pyrite) and propylitic alteration (quartz–plagioclase–chlorite–calcite–epidote–smectite±kaolinite±pyrite±chalcopyrite±magnetite). The central sector of the prospect, situated in the NE flank of the paleo-stratovolcano, is characterized by hydrothermal breccias structured towards N65E. The main mineral phases comprise quartz and abundant pyrite, sometimes with traces of As. Anomalous geochemical values of Ag, As, Bi, Hg, Se, Sb and Te coincide with high gold contents in this sector of the prospect. Jarosite and goethite are evidence of a subsequent supergene event. Based on the mineralogical characterization, we conclude the existence of a high sulfidation epithermal system in Chapi Chiara. Hypogene minerals of higher temperature in the SW sector of the prospect, such as diaspore, pyrophyllite and topaz in the AAA zone, and epidote in the propylitic alteration zone, can reveal that the system is currently in a relatively deep erosion level, suggesting its proximity in relation to the interface between a deep epithermal system and a mesothermal system.

Fusing ASTER, ALI and Hyperion data for enhanced mineral mapping

This investigation fused Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), Advanced Land Imager (ALI) and Hyperion data for detecting hydrothermal alteration minerals associated with porphyry copper mineralisation and related host-rock lithology. The distribution of iron oxide/hydroxide minerals, vegetation and clay minerals was identified based on principal component analysis, using the distinctive bands of ASTER and ALI at a regional scale. The analysis also showed that by fusing these different data sources, the discrimination of quartz-rich igneous rocks from the magmatic bedrock and the boundary between igneous and sedimentary rocks using ASTER thermal infrared bands could be made. An image map of spectrally predominant mineral assemblages in the hydrothermal alteration zones could be produced using the shortwave infrared bands of Hyperion data at a district scale. Phyllic, advanced argillic and propylitic alteration zones associated with porphyry copper mineralisation were discriminated based on the identified alteration minerals such as sericite, kaolinite, illite, alunite, chlorite, epidote and calcite. Results have proven to be effective, and in accordance with the results of field investigations. It is concluded that the methods of image and data fusion of spectral information derived from ASTER, ALI and Hyperion data can produce comprehensive and accurate information for copper resource investigations.