Propylitic Zone Research Articles

Mineral exploration and environmental impact assessment in the Jabal Hamadat Area, Central Eastern Desert, Egypt, using remote sensing and airborne radiometric data

Mineral exploration is essential for economic growth, but it must be conducted with careful consideration of health and environmental impacts. This study focuses on mapping potential mineralization areas and evaluating environmental consequences in the Jabal Hamadat area. By integrating ASTER, Landsat-9 and airborne radiometric data, the study includes: (1) identification of alteration mineral indicators including iron oxides (gossanized zone), chlorite (propylitic zone), kaolinite, sericite, montmorillonite/illite (argillic zone), and alunite (advanced argillic zone) via the Band Ratio (BR) technique; (2) preparation of a lineament density map through an automated lineament extraction technique; and (3) identification of areas with elevated F-parameter values exceeding 10. Ten areas with high mineralization potential are delineated for further exploration. Additionally, the study assesses environmental radiation exposure, finding that certain areas exceed the safe radiation limit of 1.0 mSv/year. Peak radiation levels range from 0.75 to 1.25 mSv/year, with mining sites showing the highest readings at 1.25 mSv/year and 0.64 mSv/year. These findings highlight elevated radiological hazards, emphasizing the need for comprehensive monitoring and effective mitigation strategies to protect human health and minimize environmental impact. The methodology's success in this area indicates its potential applicability to other mining areas, contributing to enhanced safety and environmental protection.

Assessment of the spaceborne EnMAP hyperspectral data for alteration mineral mapping: A case study of the Reko Diq porphyry Cu[sbnd]Au deposit, Pakistan

For over four decades, spaceborne multispectral data have played a crucial role in supporting mineral exploration and geologic mapping. The spaceborne multispectral datasets, however, have a restricted number of bands with coarse spectral resolution and, thus are very limited in mineral mapping. The advent of high-quality spaceborne imaging spectroscopic data like the Environmental Mapping and Analysis Program (EnMAP), has bridged this gap initiating a new era in global hyperspectral mineral mapping. The EnMAP satellite, operational since November 2022, covers the spectral range of 420 and 2450 nm in 224 bands, offering a spatial resolution of 30 m and a mean spectral sampling distance of 8.1 and 12.5 nm in the visible-near infrared and shortwave infrared regions, respectively. In this paper, we demonstrate the enhanced mapping capabilities of EnMAP using datasets acquired over the Reko Diq mining district, a cluster of Miocene porphyries located in Pakistan's Chagai Belt hosting an undeveloped world-class porphyry Cu-Au ± Mo deposit. The EnMAP's Level 2A data product was processed using the polynomial fitting technique to characterize the diagnostic absorption features of the alteration minerals in the Reko Diq porphyry system. This involved retrieving the minimum wavelength, depth, width, and asymmetry parameters for key absorption features and employing them interactively for mineral characterization. A diverse array of minerals were successfully mapped over the study area and validated by ground spectroscopy. This includes abundance/composition maps for white micas, chlorite, epidote, calcite, kaolinite, gypsum, jarosite, and ferric and ferrous iron minerals. The minimum wavelength of white mica was found to vary between 2195 and 2210 nm, with the shorter wavelengths (Al-rich) white mica occurring proximal to the known mineralized zones. The potassic alteration cores and the outer propylitic zones were identified by the ferrous iron and chlorite-epidote-calcite mineral maps, respectively. This study demonstrated the superiority of EnMAP hyperspectral data in delineating the alteration mineralogy and zonation pattern of porphyry copper systems. This capability can potentially contribute to the exploration of new deposits in exposed terrains worldwide.

Geological characteristics and ore‐forming conditions of the Tasikmadu porphyry Cu–Au prospect in Trenggalek, East Java, Indonesia

Tasikmadu is a newly discovered porphyry Cu–Au prospect in the eastern Sunda arc, Indonesia. This study aimed to elucidate salient diagnostic characteristics and ore‐forming conditions of the prospect. Fieldwork and various laboratory analyses for a suite of representative samples were performed for mineralogy, bulk‐geochemistry, mineral chemistry and ore fluid characterization. The study area is composed of three diorite porphyries, that is, fine‐grained, medium‐grained and coarse‐grained diorite porphyry, respectively. The intrusions are calc‐alkaline with a high Sr/Y value, which is similar to many ore‐bearing intrusions in the eastern Sunda arc. Ore mineralization occurs in quartz veins and veinlet stockwork, centred in the potassic zone, and dominated by chalcopyrite and bornite occurring in A and B veins, which cut earlier barren (EB) and M veins. The mineralization core has an average grade of 0.63 wt% Cu and 0.25 ppm Au, respectively. Outwardly, the potassic zone changes to the propylitic zone, which still bears copper in the quartz and pyrite veinlets, although the grade is low. Fluid inclusion microthermometry revealed that the A and B veins in the potassic zone formed at 464 and 390°C by hypersaline boiling fluids, respectively. The temperature temporally and spatially decreased, that is, in the propylitic zone, the quartz veinlets formed at 260–400°C. Hypogene mineralization that formed the A veins occurred at 1.5 km below the palaeosurface, indicating a relatively shallow depth as a porphyry deposit. Nevertheless, the δ34SCDT values of sulphides range from −2.0 to −0.1‰, inferring a magmatic origin. The Tasikmadu prospect shares some similarities compared with other porphyry deposits worldwide, but it also reveals unique characteristics that differ from others, for example, potassic‐altered rocks are only typified by secondary biotite without/rare secondary K‐feldspar reflecting the lack of magma contamination by continental crustal components. In addition, current surface geological features and shallow depth erosion level of the prospect may imply that the potential of Cu–Au mineralization underneath is still open to depth.

Geochemical characteristics and implications of epidote in South Dulan and Vlaska exploration greenfield in north of Bor metallogenic zone, Serbia

The Bor metallogenic belt in Serbia is a promising region for copper-gold (Cu-Au) resources, hosting numerous porphyry copper deposits, epithermal gold deposits and metallogenic prospects, such as the South Dulan and Vlaska exploration greenfield. Epidote alteration is integral to the propylitic and sodic-calcic alteration assemblages within this region. It is distinguished by the extensive occurrence of two primary epidote types: disseminated (Ep1) and veined (Ep2) epidote. In this study, comprehensive petrographic analysis reveals that in the propylitic zone, epidote mainly replaced hornblende (Ep1a) and plagioclase phenocrysts (Ep1b), coexisting with chlorite, apatite and titanite. In proximity to the potassic zone, epidote (E1c) coexists with biotite, while epidote (Ep2), chlorite, pyrite and chalcopyrite veinlets are observed near the ore body. Notably, Ep1 exhibits lower Fe and higher Mn contents in comparison to Ep2. Additionally, elements such as Ca, Al and Fe in Ep1a, and Ca, Fe, Mg, Mn and Ti in Ep1b, as well as Ca, Al, Fe and Mn in Ep1c, are introduced into the epidote through hydrothermal fluid interactions. Variations in trace element characteristics are evident among different epidotes. Specifically, Ep1a exhibits elevated Mg content (324–6050 ppm), Ep1b is notable for its high Na (22–942 ppm) and Sr (523–3075 ppm) contents, while Ep1c contains elevated K (24–445 ppm) and Na (41–103 ppm). Which suggest that disseminated epidote (Ep1) inherits the geochemical features from its precursor minerals. In comparison to disseminated epidote, epidote in veinlet exhibits higher Fe3+, Cu, Sn and REEs, along with lower contents of Pb, Sb and Sc, suggesting that these elements have been integrated into epidote through isomorphism substitution and influenced by fluids compositions, physical factors (temperature, pressure, etc.) and chemical parameters (speciation, pH, fO2, etc.), as well as mineral assemblages. Therefore, the trace element contents of Pb, Sb, Sc, Cu, Sn and REEs in epidote could serve as more appropriate indicators for mineral geochemistry in porphyry deposit hydrothermal centers.

Alteration Mineral Mapping of the Shadan Porphyry Cu-Au Deposit (Iran) Using Airborne Imaging Spectroscopic Data: Implications for Exploration Drilling

Abstract Porphyry copper deposits are associated with large alteration footprints, and alteration mapping plays a key role in the exploration of these deposits. Imaging spectroscopy is commonly deployed for exploration targeting, yet it has rarely been used to map deposit-scale alteration patterns before initiating drilling. To close this gap, the Shadan porphyry Cu-Au deposit was thoroughly studied using the HyMap hyperspectral data (visible near-infrared–short-wave infrared) at 5-m resolution corroborated by rock geochemistry, magnetometry, and laboratory spectroscopy. Shadan is a well-exposed deposit with near-perfect zonation located in the volcanic belts of eastern Iran containing >135 Mt of ore at 0.3% Cu and 0.4 g/t Au. Thirteen minerals, including white mica, Al smectite, kaolinite, ferric/ferrous minerals, biotite, actinolite, epidote, chlorite, tourmaline, and jarosite, were mapped by applying the multifeature extraction methodology. The propylitic zone was partitioned into actinolite, epidote, and chlorite subfacies. The compositions of biotite and white mica were observed to become Fe and Al rich, respectively, toward the mineralized zones. The chemistry of actinolite was observed to change from Fe to Mg rich inward, providing a new vectoring tool for porphyry copper exploration. The study provided significant information about fluid-rock interactions and the chemistry of the circulating fluids including the oxidation-reduction states and acidity. By integrating the mineral maps with other data sets using the fuzzy logic method, the promising (ore) zones were identified and used to plan the next-stage drilling. This work demonstrated that imaging spectroscopy can be effectively used to better understand porphyry systems and provide deposit-scale vectors toward the mineralized centers, facilitating drilling.

Using pyrite composition to track the multi-stage fluids superimposed on a porphyry Cu system

Abstract The Yulekenhalasu porphyry Cu-Mo deposit (0.2 Mt Cu at 1.04 wt% and 0.012 Mt Mo at 0.06 wt%) is located in the Devonian Halasu copper belt, East Junggar block, northwest China. At Yulekenhalasu, Cu and Mo mineralization commonly occurs as disseminated sulfides or veinlets in porphyry-related alteration zones. Five alteration stages have been identified, including porphyry-type alteration, i.e., sodic-calcic (stage I), potassic (stage IIa), propylitic (stage IIb), and phyllic (stage III) alteration, and widespread late Cu sulfide-bearing veins (stage IV) cross-cutting porphyry-type alteration, plus a post-ore fault-controlled argillic alteration (stage V). Stages IV and V have overprinted porphyry-type alteration (stages I–III). Anomalous concentrations of trace elements in stage IIb pyrite (e.g., Ti, Zr, Gd, and Hf) are due to the presence of micro-inclusions (e.g., zircon and rutile) in the low-temperature (~200 °C) propylitic zone. Cu, Ag, Co, and Mn, occurring as stoichiometric substitutions or as tetrahedrite inclusions in overprinting stage IV pyrite, were sourced directly from the primary hydrothermal fluid. The enrichment of distal pathfinder elements (e.g., Cr, Au, and Tl) in overprinting stage V pyrite was caused by a low-temperature (~160 °C) hydrothermal event related to regional orogenic Au mineralization. The spatial variation of Se/S in pyrite among various paragenetic stages were influenced by changes in the hydrothermal fluid composition and temperature, with the latter having the effect of decreasing pyrite Se/S. Lower Se concentrations in pyrite of stages IIb and III close to the orebody are explained by relatively higher temperatures in the locus of mineralization. This may provide a potential vectoring tool to mineralization using pyrite geochemistry in porphyry deposits. Systematic thermodynamic calibrations were applied to pyrite compositions to fingerprint the corresponding Se/S and Co/Ni ratios of fluids and further to develop a complete metallogenic model for Yulekenhalasu. The Devonian diorite porphyry generated fluids that produced the early porphyry-type alteration. High Co/Fe (average ~1 × 10–4) and Ni/Fe (average ~3 × 10–6) ratios of fluid for late Cu sulfide-bearing veins, combined with higher Se/S (average ~6 × 10–7) than orogenic Au deposits (average ~3 × 10–8), indicate that the fluids possibly derived from a Late Devonian-Carboniferous mafic intrusion. Argillic alteration assemblages forming at ca. 280 Ma host pyrite relatively enriched in Au (average 0.1 ppm, with native gold inclusions). Therefore it is likely related to a regional orogenic gold mineralizing event in the Early Permian that overprinted Devonian mineralization. Although spatially contiguous, hydrothermal alteration and hypogene mineralizing stages identified herein represent discrete episodes of hydrothermal activities at Yulekenhalasu. The multi-stage alteration features observed at Yulekenhalasu may provide insights into the complete evolutionary history of Paleozoic porphyry Cu deposit systems in the Central Asian orogenic belt. This study contributes to a better understanding of the metallogenic and exploration models of porphyry Cu deposits overprinted by multi-stage hydrothermal events, which is economically important in Phanerozoic orogenic belts.

THE THE CHARACTERISTICS OF BASE OF CONDUCTOR IN X GEOTHERMAL FIELD BASED ON THE MAGNETOTELLURIC AND WELL DATA

The X Geothermal Field in Flores, East Nusa Tenggara, has surface thermal manifestations such as hot springs, fumaroles, and alteration rocks, which indicate potential geothermal resources. This research aims to model and characterize the base of the conductor in X geothermal field as a supporting data for geothermal exploration studies. The modeling was performed using 3D magnetotelluric inversion analysis that was correlated with well data, i.e, drill cuttings, methylene blue, and Pressure and Temperature Test. According to the results, the subsurface condition of the study area consists of an argillic zone around 400-300 masl, a transition zone around 300 and 0 masl, and a propylitic zone below 0 masl. At an elevation of 400-300 masl, the base of conductor marks the boundary between the reservoir and the clay cap. The BOC distribution map reveals that the average BOC elevation is between 300 and 550 meters above sea level. The exploration potential is in the northern part with a prospect area of 3,4 km2 in research.

Mapping hydrothermal alteration of the Au-Cu deposits in the Zhenghe magmatic-hydrothermal mineralization system, SE China, using Short Wavelength Infrared (SWIR) reflectance spectroscopy

Magmatic–hydrothermal mineralization developed in Zhenghe area, where a potential of blind porphyry Cu polymetallic deposits is expected. To explore alteration characteristics and their relationship with mineralization, alteration mineral mapping with the help of SWIR reflectance spectroscopy was carried out in the Dongji Au deposit, the Maluntou Au deposit, the Shizigang Cu polymetallic deposit, and the Dongkeng volcanic basin. The results suggest that illite ± chlorite assemblage predominates in the Dongji deposit, whereas phengitic illite ± chlorite ± epidote occurred in the Maluntou deposit. Chlorite ± epidote ± actinolite developed pervasively in the Shizigang deposit. The alteration feature and ore geology indicate the Dongji and Maluntou deposits formed in a low-intermediate sulfidation epithermal environment with moderate-low temperatures. Maluntou is more likely approached to a heat source. Four alteration zones including potassic–silicic zone, propylitic zone, phyllic zone, and surficial argillic zone are divided, and a heat center is roughly inferred in the Shizigang district, suggesting a proximal porphyry-hydrothermal alteration style.A model demonstrating mineralization and alteration is established, along with mineral spectral vectors to mineralization. Illite with Pos2200 (wavelength of sericite Al-OH absorption peak position) of about 2203 nm is correlative with Au mineralization in the Dongji deposit and phengitic illite with Pos2200 ranging from 2215 nm to 2219 nm is the product of metallogenesis in the Maluntou deposit. Illite with Pos2200 of approximately 2205 nm–2206 nm in the Nanyuan Formation and illite with Pos2200 of about 2207 nm in the Huangkeng Formation are formed in the non-mineralization stage or weathering. Muscovite with the Pos2200 of roughly 2206 nm has the potential to be an orebody vector in the Shizigang district. Pos2250 (wavelength of chlorite Fe-OH absorption peak position) variation in the Shizigang district indicates the location of drill hole ZK1-1 is approximal to the hydrothermal center.Shizigang Cu, Maluntou Au, Dongji Au, and other deposits in Zhenghe are probably part of an integrated metallogenic system with epithermal-porphyry features. High-intensity magmatic-hydrothermal activity indicates the potential for deep prospecting in the region.

Indication Of Hydrothermal Alteration Based On Petrography Of Granit Garba (KGR), Tanjung Beringin Village, Muaradua District, South Sumatera

The research was conducted in Tanjung Beringin Village, Muaradua District, South OKU Regency, South Sumatra. The location of this research is geologically located in the basement of the South Sumatra Basin which composes the Garba Mountains, namely Granit Garba. Granit Garba is an intrusion rock with the youngest age among the basement rocks forming the South Sumatra Basin. The lithology that composes this formation is a granitoid rock with interesting constituent mineral characteristics and there are indications of hydrothermal alteration processes that affect rock formation. The characteristics and hydrothermal alteration of these granitoid rocks can be identified using petrographic analysis of rock thin sections. Based on the petrographic analysis, it is interpreted that there are two groups of granitoids that make up Granit Garba. The two groups of granitoids are quartz monzonite and granodiorite. The difference between the two types of rock lies in the composition of the main mineral constituents. Quartz monzonite is a rock with minimal quartz composition and relatively the same percentage of plagioclase and alkali feldspar. Meanwhile, granodiorite has more quartz composition than quartz monzonite with relatively more plagioclase minerals than alkali feldspar minerals. The appearance of the thin section in the petrographic analysis of the rock also shows the influence of hydrothermal alteration as evidenced by the presence of secondary minerals. These secondary minerals form associations that occur in the phylic and propylitic zones. The phyllic zone is indicated by the presence of sericite, chlorite, and opaque minerals in the form of pyrite, while the propylitic zone has an assemblage of epidote, chlorite, and calcite minerals.

Karakteristik Mineralisasi Endapan Emas Epitermal Sulfidasi Rendah di Daerah Mekarbakti, Kecamatan Bungbulang, Kabupaten Garut, Provinsi Jawa Barat

The southern mountains of western Java have been known to have large gold deposit potential. The Mekarbakti area, located in Garut regency, is known to have gold-bearing quartz veins, but the distribution and characteristics of these veins are not well recorded. The purpose of this study is to determine the geological conditions of the deposits and the characteristics of the epithermal deposits in the study area, in term of alteration, ore mineralization, vein texture, and ore geochemistry. Field work includes random sampling of veins from surface outcrops and cores. Laboratory analysis includes mineragraphic, geochemical analysis by means of Fire Assay Atomic Absorption Spectrophotometry (FA-AAS) and Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) . The lithology of the Mekarbakti area is composed of volcanic rocks including andesite lava, andesite intrusion and pyroclastic rocks such as breccia and tuff. The mapping results show that the hydrothermal alteration that developed is divided into three zones of alteration type, namely the silicification zone (silica + - clay), the argillic zone (kaolinite + - smectite - illite) and the propylitic zone (chlorite - smectite - epidote - illite). Quartz texture is generally dominated by brecciated, colloform, comb, lattice bladed and cockade textures. The texture interpretation of the veins shows a crystalline quartz zone, which is enriched in base metals such as galena, sphalerite and chalcopyrite and a crustiform – colloform zone which usually contains gold and silver. Veins in the study area contain the elevated grades of 3.21 ppm Au and 75.5 ppm Ag.

Geochemistry and magnetite mineral properties in a porphyry copper prospect in A‐type granitoids: A case study from the Karbi Hills of Northeast India

This paper discusses the porphyry copper mineralization in A‐type granitoids from the Precambrian shield of the Karbi Hills (Mikir Hills), NE India. The prospective zone lies in the Kuthori‐Bagori of Kaziranga locality of the north Karbi Hills. The host granitoids are characterized by intermediate to high SiO2 (66.30–72.97 wt.%), Na2O (up to 4.90 wt.%), Ba (up to 1,943 ppm), Zr (up to 410 ppm), Y (up to 70 ppm) and Al2O3 (up to 14.77 wt.%) with low concentrations of CaO (up to 1.53 wt.%), and Cu (up to 32.41 ppm) which suggest a consistent granodiorite‐monzogranite host composition, an intraplate emplacement, A‐type chemistry, shoshonitic to high‐K calc‐alkaline and a predominant metaluminous character. Minerals in the investigated granitoids show hypogene alteration features similar to ideal porphyry style mineralization. Remnants of early chalcopyrite‐bornite‐magnetite (Magnetite‐I) veins have been preserved in the distant propylitic zone. The central core zone of potassic alteration shows the dominance of pyrite‐chalcopyrite‐magnetite (Magnetite‐II) assemblages. Mineral chemistry confirms the presence of two types of magnetites: magmatic (Mag‐I) and hydrothermal (Mag‐II). Mag‐I is octahedral, less commonly cubic, or irregular. It has a porous core with trellis‐type ilmenite exsolution lamellae. Mag‐II is non‐porous, devoid of ilmenite exsolution lamellae, has irregular to distinctly octahedral crystal habit and contains micro‐inclusions of pyrite, chalcopyrite, aluminosilicates, manganite and apatite. The progressive chemical purification of igneous magnetite, exacerbated by hydrothermal re‐equilibration, has resulted in a significant reduction in trace element contents such as Ti, Al, Mg, Zn and Cr, and a significant increase in iron content from 89 to ~94 wt.%. A combination of [Ni/(Cr + Mn) vs. Ti + V], and [(Ca + Al + Mn) vs. Ti + V] variation diagrams and upper threshold concentrations for the Kuthori‐Bagori ore effectively separates Mag‐I and Mag‐II. Our field, petrographic and geochemical data indicate that the Kuthori‐Bagori of Kaziranga granitoid of the Karbi Hills (Mikir Hills) in NE India is an ideal location for porphyry copper mineralization.

Origin of the Dongbulage Mo–Pb–Zn deposit in the Great Hinggan Range, northeast China: Geological, molybdenite Re–Os dating, fluid inclusion, and C–H–O–S–Pb isotope constraints

The Dongbulage porphyry Mo–Pb–Zn deposit is located in the Huanggang–Ganzhuermiao polymetallic district (HGD) in the southern part of the Great Hinggan Range in northeast China. The Dongbulage deposit is hosted by granite porphyry, and the wall rock alteration can be divided into quartz–potassic, quartz–sericite, and propylitic zones. The hydrothermal activity in the deposit can be divided into five stages, with molybdenite and Pb–Zn ore occurring mainly as veins and veinlets in stages II and III, respectively. The fluid inclusion (FI) types include liquid-rich (L-type), vapor-rich (V-type), and daughter mineral-bearing (S-type) FIs. Based on the combination of FI types and their temperatures and salinities, it is inferred that fluid boiling and incorporation of meteoric water were key factors in the precipitation of Mo and Pb–Zn, respectively. Hydrogen and O isotope data for quartz, and C and O isotope data for calcite indicate that the ore-forming fluids were primarily magmatic in origin, and were mixed with meteoric waters during their evolution. The S and Pb isotope data, along with the mineral paragenesis, suggest that molybdenite and chalcopyrite which precipitated during stage II were derived mainly from magmatic–hydrothermal fluids, whereas arsenopyrite, sphalerite, and pyrite that precipitated during stage III were strongly affected by the incorporation of surrounding strata materials. Rhenium–Os dating of molybdenite indicates that mineralization in the Dongbulage deposit occurred at 162.1 ± 1.3 Ma (n = 6; MSWD = 1.4). The results, combined with data from other deposits in the region of this age, indicate that important mineralization occurred in the HGD during 165–155 Ma.

Application of per-pixel and sub-pixel unmixing methods on ASTER images to map hydrothermal alterations in a highly metamorphosed terrain: a case of the Musina copper deposit field

This study focuses on mapping hydrothermal alterations in Musina Copper Deposit Field which is characterized by unique concentric zonation of hydrothermal alterations from an outer zone of sericitization (phyllic) followed by inward zones of chloritization and epidotization (propylitic). Per-pixel and mixture tuned matched filtering (MTMF) sub-pixel unmixing methods were applied on ASTER data to map hydrothermal alterations. False colour composite (FCC) generated from combination of propylitic, phyllic and host rock index was effective in delineating alteration zones. The spatial distribution of alteration group minerals: chlorite–epidote and sericite–muscovite from MTMF classification correspond with their associated alteration zones. Correlation coefficient (R 2) was utilized to assess accuracy of the results by comparing MF scores of alteration minerals with copper concentrations. R 2 was 0.78 for chlorite–epidote and 0.69 for sericite– muscovite. Copper concentration levels increase towards chlorite–epidote region which represents the inward propylitic zone. Following the geometry and alteration zonation, follow-up targets were generated.

Geology and geochronology of the Don Javier Cu-Mo porphyry deposit, southern Peru

The Don Javier porphyry Cu-Mo deposit is located in the Yarabamba district of the Arequipa region, Peru, which represents the northwestern end of the Paleocene-early Eocene Cu belt of the central Andes, extending from northern Chile into southwestern Peru. The deposit occurs around the contacts of a dacite porphyry stock emplaced into the pre-mineralization and Yarabamba granodiorite batholith. The intrusions display a telescoped sequence of alteration, from shallow sericitic to deeper chloritic-sericitic, with minor remnant potassic assemblages, which are surrounded by propylitic zones. EB-, M-, EQ-, SQ-, and D-type veinlets occur in all alteration zones. The higher Cu and Mo grades are mainly associated with the widely distributed sulfide-quartz veinlets within the potassic and chlorite-sericite overlapping zones. The mineralized zone measures ∼500 m in width (NE-SW) by ∼800 m in length (NW-SE). Uranium-Pb zircon ages show that the Yarabamba granodiorite plutons were emplaced at ∼ 64.6 Ma and subsequently intruded by the inter-mineralization dacite porphyry intrusions at ∼ 59.9 to 59.5 Ma. Molybdenite Re-Os ages indicate that the deposit formed between ∼ 60.5 and 59.6 Ma. Younger molybdenite Re-Os ages (∼45.4 to 44.4 Ma) obtained in the deep parts of the altered rocks suggest that the deposit might have been overprinted by later hydrothermal activity in the Eocene. The success of exploration at Don Javier emphasizes that traditional methods such as geologic and geophysical mapping followed by timely drilling tests can still be effective in a mature metallogenic belt.

Host rock petrology, hydrothermal alteration characteristics & ore mineralogy of porphyry copper-gold deposit, Brambang, Lombok, West Nusa Tenggara Indonesia

Several world-class porphyry copper–gold deposits/prospects have been discovered in the eastern Sunda arc. One copper–gold prospect area is located at Brambang, Sekotong District, West Lombok Regency, West Nusa Tenggara Province, Indonesia This study is aimed to understand a preliminary geological framework, which characterizes the Brambang deposit in terms of the host rock, hydrothermal alteration characteristics, and ore mineralogy studies of the deposit. Fieldworks and several laboratory analyses were performed including petrography, ore mineralogy and X-ray diffraction (XRD). Host rock was dominated by volcanic rocks consisting of dacitic volcanic rock, diatreme breccia, and diorite intrusion. The hydrothermal alteration is characterized by argillic alteration (kaolinite-illite-smectite), propylitic (chlorite-epidote-calcite), and potassic (quartz-biotite-actinolite-magnetite), with the presence of sulfide minerals such as pyrite (FeS2), chalcopyrite (CuFeS2), and chalcocite (Cu2S), and the oxide minerals such as magnetite (Fe3O4), and hematite (Fe2O3). The alteration zone stage in the study area begins with forming a quartz-biotite-magnetite (potassic zone) formed at a high temperature of around 300–360 °C and at pH 7–8. This stage is followed by forming a chlorite-epidote-calcite (propylitic zone) outside the potassic zone, at a temperature range of 290–340 °C and pH of 5–6, which indicates a hydrothermal system cooling process. Then, due to the increasing influx of meteoric fluid that enters the fractures formed due to fault activity, a quartz-kaolinite-illite (argillic zone) is formed with a temperature range of 130–210 °C and pH 4–6. The presence of diatreme breccia and stockwork within the mineralization in the Brambang deposit supported the theory related to porphyry copper–gold deposits.

Hybrid Fuzzy-Analytic Hierarchy Process (AHP) Model for Porphyry Copper Prospecting in Simorgh Area, Eastern Lut Block of Iran

The eastern Lut block of Iran has a high potential for porphyry copper mineralization due to the subduction tectonic regime. It is located in an inaccessible region and has harsh arid conditions for traditional mineral exploration campaigns. The objective of this study is to use Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) remote sensing data for porphyry copper exploration in Simorgh Area, eastern Lut block of Iran. Hydrothermal alteration zones such as argillic, phyllic and propylitic zones associated with porphyry copper systems in the study were identified using false color composition (FCC), band ratio (BR), principal component analysis (PCA) and minimal noise fraction (MNF). The thematic alteration layers extracted from FCC, BR, PCA and MNF were integrated using hybrid Fuzzy-AHP model to generate a porphyry copper potential map for the study area. Four high potential zones were identified in the central, western, eastern and northeastern of the study area. Fieldwork was used to validate the approach used in this study. This investigation exhibits that the use of hybrid Fuzzy-AHP model for the identification of hydrothermal alteration zones associated with porphyry copper systems that is typically applicable to ASTER data and can be used for porphyry copper potential mapping in many analogous metallogenic provinces.

Distribution of hypogene alteration and fluid evolution in the Los Humeros Geothermal Field (Puebla, Mexico): Multiple sourced fluids, interrelations, and processes in a superhot system

The Los Humeros Geothermal Field (LHGF) is one of the highest producing geothermal areas in Mexico. This paper aims essentially to determine high-resolution patterns of distribution of hypogene alteration assemblages and the distribution of temperatures in space and time of geothermal fluids in the LHGF. The zoning of hypogene alteration assemblages in the LHGF consists of (1) shallow advanced argillic alteration assemblages that grade into (2) argillic and (3) zeolitic assemblages with depth, followed by (4) low-temperature and (5) high-temperature propylitic, and (6) deep high-temperature high-silica advanced argillic alteration assemblages. The distribution of deep advanced argillic alteration assemblages is associated with the occurrence of acidic supercritical fluids prior to their deep boiling. Capping these, high-temperature propylitic assemblages are associated with the occurrence of subcritic brines (barely exceeding 13 wt% NaCl equiv.) that stemmed from magmatic supercritic fluids (upon degassing and/or conductive cooling) and that were diluted by deeply circulated and thermally equilibrated meteoric water. Conductively cooled subcritic fluids, which eventually kept being diluted on their way to the surface, would be likely associated with the generation of shallow low-temperature propylitic assemblages. Relatively fresh meteoric water might have been increasingly relevant in such dilution as upwelling fluids neared the surface. Shallow boiling occurred mostly between high- and medium-temperature propylitic zones, and generated acidic vapors that eventually condensated in the phreatic water table and, in part, in the argillic alteration zone. Shallow hypogene advanced argillic (and argillic) alteration consisting of kaolinite, platy alunite, native sulfur and the newly found cuprocopiapite occurred in steam-heated grounds. Fluid inclusion and present-day geothermal fluid data allow to introduce relative time as a variable in the characterization of hydrothermal fluids in the LHGF. These sets of temperature data allow to independently determine patterns of temperature distribution as isotherms. Concave shapes in isotherms are interpreted to spearhead preferential passageways for hydrothermal fluids. Some areas (for instance, in the southern part of the LHGF) record relatively stable passageways through time, but these may significantly shift their positions in other areas. Stable passageways, apparently undisturbed by geothermal exploitation, may identify robust portions of the system that ensure a long-lasting exploitation. They also correspond to sound inputs of high-salinity and hot magmatic fluids, which may be sandwiched between cooler low-salinity fluids, dominantly meteoric in origin, and collectively make a case for convection (and partial mixing). Also, we determined that “older” inclusion fluids are ∼50 °C higher than “younger” fluids from geothermal wells, but such decrease can be compatible with the cooling down of the system due to geothermal exploitation. Therefore, such differences in temperature do not necessarily reflect an actual cooling in the system.

Application of Landsat 8 Image in An Assessment of Hydrothermal Alteration Mapping in Dense Vegetation: A Case Study from Kokap Area, Kulon Progo

DOI:10.17014/ijog.9.1.45-60Several researchers through geochemical analysis have proven the presence of gold mineralization in Kokap, Kulon Progo, as a result of hydrothermal alteration. Alteration mapping with optical remote sensing images in tropical areas is very difficult due to atmospheric conditions, dense vegetation cover, and rapid weathering. This study aims to assess the ability of Landsat 8 images in the mapping of hydrothermal alteration in Kokap, Kulon Progo, with the Principles Component Analysis (PCA) method. Three conventional machine learning methods, including artificial neural network (ANN), maximum likelihood classification (MLC), and support vector machine (SVM) were compared to find an optimal classifier for hydrothermal alteration mapping. The experiment revealed that the MLC method offered the highest overall accuracy. Two alteration zones were mapped, i.e. argillic zone and propylitic zone. The comparison results showed that the MLC classification of band ratio images of 5:2 and 6:7 yielded a classification accuracy of 56.4% and kappa coefficient of 0.36, which was higher than those of other machine learning methods and band combinations. The combination of Landsat 8 with DEM succeeded in increasing accuracy to 59.5% with kappa coefficient of 0.4.

Comparison of Different Multispectral Images to Map Hydrothermal Alteration Zones in Kokap, Kulon Progo

Using remote sensing data for hydrothermal alteration mapping beside saving time and reducing cost leads to increased accuracy. In this study, the result of multispectral remote sensing tehcniques has been compare for manifesting hydrothermal alteration in Kokap, Kulon Progo. Three multispectral images, including ASTER, Landsat 8, and Sentinel-2, were compared in order to find the highest overall accuracy using principle component analysis (PCA) and directed component analysis (DPC). Several subsets band combinations were used as PCA and DPC input to targeting the key mineral of alteration. Multispectral classification with the maximum likelihood algorithm was performed to map the alteration types based on training and testing data and followed by accuracy evaluation. Two alteration zones were succeeded to be mapped: argillic zone and propylitic zone. Results of these image classification techniques were compared with known alteration zones from previous study. DPC combination of band ratio images of 5:2 and 6:7 of Landsat 8 imagery yielded a classification accuracy of 56.4%, which was 5.05% and 10.13% higher than those of the ASTER and Sentinel-2 imagery. The used of DEM together with multispectral images was increase the accuracy of hydrothermal alteration mapping in the study area.

Chlorite mineralogy, geochemistry and exploration implications: A case study of the Xiaokelehe porphyry Cu-Mo deposit in NE China

The recently discovered Xiaokelehe porphyry Cu-Mo deposit (PCD) is situated in the northern part of the Great Xing’an Range in NE China. At Xiaokelehe, chlorite-illite alteration is characterized by chlorite, illite, disseminated chalcopyrite and pyrite assemblages that are widely developed in the granodiorite porphyry. The illite is altered from plagioclase or K-feldspar, and the chlorite from both igneous and hydrothermal biotite. The chlorite can be divided into three types (Chl1, Chl2 and Chl3): Chl1 is locally developed in the deeper part of the granodiorite porphyry, and is altered from hydrothermal biotite; Chl2 is pervasively distributed in the deeper part of the granodiorite porphyry, and is altered from igneous biotite and associated with abundant disseminated Cu-Fe-sulfide mineralization; Chl3 is widely developed in the shallower part of the granodiorite porphyry, and is altered from igneous biotite. Chl3 is overprinted by phyllic alteration and associated with minor disseminated Cu-Fe-sulfide mineralization. These Xiaokelehe chlorites resemble the chlorites from typical sericite-chlorite-calcic alteration (SCC) in PCDs, and are the first reported SCC-related chlorites in the Great Xing’an Range.Mineral geochemical results show that Chl1 has relatively high FeO, Mn, Ti, Li and Zn contents. Chl2 has relatively high FeO, Mn, Co, Ni, Zn and Sr contents, and Chl3 has relatively high MgO, K and Ni contents. These geochemical differences are likely controlled by temperature (e.g., for Ti), precursor minerals (e.g., for FeO and MgO) and fluid compositions (e.g., for FeO, MgO, Mn, Co and Zn). All Chl1 to Chl3 are classified as trioctahedral chlorite. The Fe-Mg, Tschermark and di-trioctahedral substitution mechanisms may have controlled the chemical differences of the Xiaokelehe chlorites. Empirical thermometer yielded chlorite formation temperatures of 209–314 °C, indicating that the Xiaokelehe chlorites were formed from intermediate-high temperature hydrothermal fluids. Compared with the chlorites from propylitic zones in other PCDs, the Xiaokelehe chlorites have higher FeO, Ti, V, Zn and Ga contents and Fe/(Fe + Mg) ratio, as well as lower MgO, K, Co and Sr contents, which distinguish chlorites in the SCC zone from those in the propylitic zone. Such differences may have also been influenced by temperature, and the protolith and fluid compositions. Compared with typical metamorphic chlorites, the Xiaokelehe chlorites have lower FeO content but higher MgO and Zn contents, of which the Zn difference is likely influenced by the fluid chemistry. We propose that the presence of Chl3 can be used as an effective vector toward mineralized zone. In addition, chlorite Mn and Zn contents in the mineralized zone are clearly higher than those away from it, and thus the chlorite Mn and Zn contents can also be potential exploration vectors at Xiaokelehe.