Resource Geology最新文献

{"title":"Genesis of Harizha Ag–Pb–Zn deposit in the eastern Kunlun Orogen, NW China: Evidence of fluid inclusions and C–H–O–S–Pb isotopes","authors":"Xingzhu Fan, F. Sun, Chenghan Xu, Wei Xin, Ying-chao Wang, Yong Zhang","doi":"10.1111/rge.12256","DOIUrl":"https://doi.org/10.1111/rge.12256","url":null,"abstract":"The Harizha Ag–Pb–Zn deposit is located in the eastern part of the eastern Kunlun Orogen, NW China. Two episodes including five paragenetic stages of vein mineralization has been recognized for the Harizha Ag–Pb–Zn deposit through petrographic observation: quartz + pyrite + arsenopyrite (Stage I), quartz + pyrite + chalcopyrite + pyrrhotite (Stage II), quartz + pyrite + chalcocite + pyrrhotite + sphalerite + galena + pyrargyrite (Stage III), quartz + calcite + pyrite + tetrahedrite + pyrolusite (Stage IV), and calcite + covellite + malachite + goethite + graphite (Stage V). In the quartz or calcite three types of fluid inclusions (FIs) were identified: L‐type, C‐type, and S‐type. The S‐type inclusions are only found in quartz in the wall rocks. The C‐type inclusions occur in quartz from early episodes (Stage I and II). The FIs from the early episodes homogenized at 240–320°C, with salinities of 9–12 wt.% NaCl equivalent. The ore‐forming fluids at the early episodes belong to an H2O–CO2–CH4–NaCl system. The FIs from late episodes (Stage III and IV) homogenized at 140–240°C, with salinities of 2–8 wt% NaCl equivalent. The ore‐forming fluids from the late episodes are dominated by an H2O–NaCl fluid system. The HO and CO isotopic compositions of quartz and calcite indicate that the ore‐forming fluids were derived from a primary magmatic‐hydrothermal system, with subsequent meteoric water involvement at a later stage. Sulfides have δ34S values of −3.7 to –1.0‰, and 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios ranging from 18.381 to 18.425, 15.661 to 15.683, and 38.498 to 38.677, respectively. These likely suggest a magmatic sulfur affinity combined with the ore features, mineral associations, alteration characteristics, ore‐forming environment, and fluid evolutionary process. We conclude that the Harizha Ag–Pb–Zn deposit is a typical medium‐low temperature hydrothermal deposit.","PeriodicalId":21089,"journal":{"name":"Resource Geology","volume":"124 1","pages":"177 - 201"},"PeriodicalIF":1.4,"publicationDate":"2021-03-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88027969","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochemistry and mineralogy of the sebkha Oum El Khialate evaporites mixtures, southeastern Tunisia","authors":"E. Essefi","doi":"10.1111/rge.12264","DOIUrl":"https://doi.org/10.1111/rge.12264","url":null,"abstract":"This work is meant to study the variation of geochemistry and mineralogy of three salts recuperated from brines of the sebkha Oum El Khialate based on XRF, X‐ray diffraction (XRD), and Fourier transform infrared (FTIR) analyses. Elemental analyses indicate enrichment with major element having an economic interest such as potassium. Compared to standards, minor elements analyses yield high concentrations of hazardous elements such as Cd and Cr, and represent a threat for human consumption. XRD and FTIR analyses display a variable mineralogy along the evaporation path including minerals that are specific for this sebkha, such as vaterite (CaCO3), potassium pentasulphate (K2S5O16), thenardite (Na2SO4), beryllium sulfate (BeSO4), brucite (Mg(OH)2), and mirabilite (Na2SO4·10 H2O). The geochemistry and mineralogy of recuperated salts prove the relevance of the sebkha Oum Khialete as a potential ore resource to be used in industry and agriculture.","PeriodicalId":21089,"journal":{"name":"Resource Geology","volume":"1 1","pages":"242 - 249"},"PeriodicalIF":1.4,"publicationDate":"2021-03-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81912715","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"K–Ar geochronology of orogenic gold mineralization in the Vangtat gold belt, southeastern Laos: Effect of excess argon in hydrothermal quartz","authors":"Patthana Bounliyong, T. Itaya, A. Arribas, Yasushi Watanabe, H. Wong, T. Echigo","doi":"10.1111/rge.12258","DOIUrl":"https://doi.org/10.1111/rge.12258","url":null,"abstract":"The Thongkai‐Ok gold deposit is one of several actively mined deposits in a newly discovered orogenic gold belt in southeastern Laos. At a district scale, gold mineralization occurs within the Vangtat shear zone, one of the tectonic structures of the Poko suture zone that marks the collision between the Indochina Terrane and the Kontum Massif in southern Laos‐central Vietnam. High grade gold mineralization is associated with quartz–pyrite–white mica veins and silicified zones up to 10 m thick, hosted by strongly deformed and sheared pelitic schist. Lower‐grade gold mineralization occurs in a graphite–carbonate–quartz–sulfide hydrothermal alteration envelope that grades into sub‐economic/barren altered pelitic schist. The objective of this study is to establish the age of mineralization in the Vangtat orogenic gold belt by K–Ar dating of hydrothermal white mica in the gold‐bearing quartz‐sulfide veins in order to better understand its spatial and temporal relation to other gold deposits in Southeast Asia and to regional tectonic events. Three‐white mica bearing quartz–pyrite samples were collected from the open pit at Thongkai‐Ok. The dominant white mica phase in the samples is 2M1 muscovite and the K2O content measured by electron microprobe techniques in individual white mica crystals ranged between 8.61 and 9.79 wt%. Two of the three vein samples were separated by gravity settling into four size fractions, <2, 2–4, 4–10, and 10–40 μm, respectively. The results of potassium measurements by flame photometry in the K–Ar sample aliquots show a range in potassium content which reflects the amount of quartz present in each sample as an impurity. With one exception, a correlation was observed between potassium concentration in the samples, including the size fraction separates, and the calculated K–Ar age. The large range of calculated ages, from 348 to 206 Ma, is interpreted to reflect excess argon contained in fluid inclusions in the hydrothermal quartz present in the analyzed samples. We interpret the youngest age of the quartz‐free samples, 206 ± 4 Ma, as closest to the age of mineralization in the Vangtat gold belt. The age could be as young as ~170 Ma if the age versus potassium content relation is extrapolated to the average potassium content of white mica in the samples analyzed.","PeriodicalId":21089,"journal":{"name":"Resource Geology","volume":"54 1","pages":"161 - 175"},"PeriodicalIF":1.4,"publicationDate":"2021-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86253375","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A magmatic‐hydrothermal origin of the Xinfang gold deposit, Liaodong Peninsula, China, revealed by in‐situ S–Pb isotopes and trace element analyses of pyrite","authors":"Bing Yu, Qingdong Zeng, H. Frimmel, Lingli Zhou, S. Mcclenaghan, Foteini Drakou, Yongbin Wang, Peiwen Chen, C. Yu","doi":"10.1111/rge.12257","DOIUrl":"https://doi.org/10.1111/rge.12257","url":null,"abstract":"The Xinfang deposit is a large gold deposit (>20 t of Au) on the southern edge of the Liaodong Peninsula, China. A total of 37 gold‐bearing orebodies are identified along NS‐ and NW‐striking faults and are mainly hosted by the Archean and Neoproterozoic metamorphic rocks. Three stages of hydrothermal mineralization are distinguished, including Stage I of dominant quartz ± pyrite (Py1), Stage II of quartz‐polymetallic sulfide (Py2), and Stage III of quartz‐calcite ± pyrite (Py3). Gold primarily occurs at the Stage II in association with intensive silicification, pyritization, and sericitization. Here, we report on high‐precision in‐situ LA‐MC‐ICP‐MS analyses of S and Pb isotopic compositions of the sulfide minerals and LA‐ICP‐MS analyses of trace element signature of the pyrite from the Xinfang gold deposit. The δ34S values of the sulfides range from 1.3 to 5.3‰, which is consistent with a magmatic origin of S. The sulfides yield 208Pb/204Pb, 207Pb/204Pb, and 206Pb/204Pb ratios of 37.497–37.773, 15.323–15.410, and 17.004–17.229, respectively, which deviate from the values of the wall rocks, suggesting an external Pb source. The in‐situ LA‐ICP‐MS spot analyses of the pyrite reveals that gold occurs in two generations of pyrite (Py2 and Py3) but at low concentrations (≤0.06 ppm for Py2, ≤0.24 ppm for Py3). Visible gold, however, only occurs in the Stage II assemblage as inclusions in pyrite and quartz, and is distributed along the margins or within the fractures of the sulfides. The Py2 shows high Co, Ni, and As concentrations and is depleted in other trace elements typical of a magmatic‐hydrothermal derivation. In contrast, Py3 exhibits low concentrations in most trace elements. Trace element mapping of Py2 revealed correlations between Fe and Co, as well as Ni and As, indicating their couped substitution in the pyrite structure. The available geological, petrographic and geochemical data consistently suggest that the Xinfang gold deposit formed during the Early Cretaceous by hydrothermal fluids of magmatic contribution.","PeriodicalId":21089,"journal":{"name":"Resource Geology","volume":"53 1","pages":"144 - 160"},"PeriodicalIF":1.4,"publicationDate":"2021-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87476123","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Estimation and comparison of the environmental impacts of acid mine drainage‐bearing river water in the Bor and Majdanpek porphyry copper mining areas in Eastern Serbia","authors":"D. Adamović, D. Ishiyama, S. Dordievski, Y. Ogawa, Z. Stevanović, H. Kawaraya, Hinako Sato, L. Obradović, Vladan Marinković, J. Petrović, V. Gardić","doi":"10.1111/rge.12254","DOIUrl":"https://doi.org/10.1111/rge.12254","url":null,"abstract":"Mining activities in the Bor and Majdanpek mining areas in Eastern Serbia started in 1903 and 1961, respectively. Environmental problems in the Bor mining area began after the opening of the Bor mine. Long‐term pollution of river water in the Bor and Majdanpek mining areas has an environmental impact on East Europe because all of the river water from these mining areas flows into the Danube River. However, the sizes of areas with pollution and the differences between the environmental impacts of the Bor and Majdanpek mining areas are not clear. In order to determine the effects of mining activities on river water in the study area, creation of geochemical maps showing the distributions of sulfate, heavy metals, and arsenic; estimation of threshold values to discriminate anomalous values from background values; and comparison of the environmental impacts of the two mining areas were carried out. High concentrations of SO42−, Fe, As, Cu, and Mn were found in the Bor River, Krivelj River, and Bela River located in the Bor mining area. These rivers are characterized by acidic pH ranging from 2.9 to 6.2. High concentrations of these components were also measured in the Small Pek River and the upper reach of the Pek River. These rivers are located in the Majdanpek mining area and are characterized by weakly alkaline pH (7.3–8.4). The acidic river water in the Bor mining area transports large quantities of heavy metals and arsenic downstream (6,900 t/year of Fe, 42 t/year of As, 910 t/year of Cu, and 187 t/year of Mn). On the other hand, the weakly alkaline river water in the Majdanpek mining area transports smaller quantities of heavy metals and arsenic downstream (160 t/year of Fe, 0.1 t/year of As, 6 t/year of Cu, and 272 t/year of Mn). The environmental impact of the Bor mining area is significantly larger than that of the Majdanpek mining area. In addition, on the basis of the distribution of anomalous values in river water, pollution caused by mining activities reaches the Danube River, which is located more than 100 km from the Bor and Majdanpek mining areas. Concentrations of SO42−, Fe, As, Cu, and Mn in the Bela River in the Bor mining area have been greatly decreased after mixing of acidic polluted water of the Bela River with water of the Timok River containing a high bicarbonate concentration. This fact suggests that river water in the Bor and Majdanpek mining areas has sufficient capacity for neutralization. Considering appropriate countermeasures of environmental reclamation, such as artificial neutralization at some important sources of waste water before discharging the waste water from the mining sites, there is a possibility for environmental reclamation in both mining areas because unpolluted river water in the study area has sufficient capacity for neutralization in a natural system.","PeriodicalId":21089,"journal":{"name":"Resource Geology","volume":"10 1","pages":"123 - 143"},"PeriodicalIF":1.4,"publicationDate":"2021-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79245270","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The magmatic–hydrothermal evolution of the San Pedro porphyry Cu‐(Mo) deposit: Implications for the metallogenesis of the Permian magmatism in the western margin of Gondwana","authors":"A. Gómez, T. Ulrich, N. Rubinstein","doi":"10.1111/rge.12251","DOIUrl":"https://doi.org/10.1111/rge.12251","url":null,"abstract":"The San Pedro porphyry Cu‐(Mo) deposit, located in the San Rafael Massif (Argentina), is characterized by multiple stockwork vein generations developed in a subvolcanic intrusion with porphyry‐type alteration and mineralization, as well as associated polymetallic veins. Previous works reveal that the intrusive rocks related to the San Pedro porphyry (263 Ma) show comparable trace element signatures to giant porphyry deposits elsewhere (i.e., high Sr/Y and low Y). The fluid inclusions investigated in this study show that typical early, high‐temperature magmatic fluids (up to 685°C; 81.3 wt% equiv. NaCl) evolved to lower‐temperature, moderately saline fluids (up to 454°C; 52.4 wt% equiv. NaCl) due to fluid–rock interaction. The waning stage of the system is characterized by secondary, aqueous inclusions that represent dilution by meteoric fluids (up to 390°C, 16.9 wt% equiv. NaCl). Fluid inclusions were studied from two veinlet generations (A and B veinlets) related to potassic alteration and analyzed by LA‐ICP‐MS. The trace element signatures in the fluid inclusions suggest that there were two pulses of magmatic fluids that subsequently evolved under similar physicochemical conditions. The Cu concentration in the earliest fluid is between 0.3 and 0.85 wt% and within the concentrations found in other mineralized porphyry systems in the world. However, in contrast to economic porphyry systems, where a significant change in Cu concentration during fluid evolution is observed, there is no distinct change in the fluid Cu concentration at the San Pedro deposit, which would indicate that Cu and Mo precipitation was ineffective in the hydrothermal system.","PeriodicalId":21089,"journal":{"name":"Resource Geology","volume":"17 1","pages":"104 - 93"},"PeriodicalIF":1.4,"publicationDate":"2021-01-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78514404","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Significance of radioelements distribution in the Precambrian rocks of Jabel Sayid, western Saudi Arabia, using spectrometric and geochemical data","authors":"H. A. Abd El‐Naby, Y. Dawood, A. A. Sabtan, Mahmood S. Al Yamani","doi":"10.1111/rge.12253","DOIUrl":"https://doi.org/10.1111/rge.12253","url":null,"abstract":"In situ gamma‐ray spectrometry measurements were carried out using RS‐230 BGO spectrometer over an area of 9.4 km2. One hundred and seventy eight spectrometric points were collected along parallel profiles with spacing 325 m in the Easting X direction and Northing Y direction. The results are treated statistically to determine the minimum, maximum, arithmetic mean (X), SD (S), and coefficient of variability (CV %). The spectrometric survey revealed the presence of radioactive zones in the aplite‐pegmatite with maximum eU content of 1,550 ppm and eTh of 7,974 ppm, whereas alkali granite has an average eU content of 12 ppm and eTh of 34 ppm. Felsite has an average eU and eTh close to that of alkali granite, 11 and 32 ppm, respectively. Pegmatite veins cutting alkali granite have high values of eU and eTh, an average of 34 and 101 ppm, respectively. The metamorphosed volcanic rocks of the Mahd Group demonstrate the lowest radioactivity with an average eU content of 0.8 ppm and eTh of 1.6 ppm. These rocks partly show evidences of post‐magmatic alteration processes, for example, silicification, sericitization, and oxidation. Excluding metavolcanics, the strong positive correlation between eU and eTh for the different rock varieties reflects their geochemical coherence during magma crystallization and indicates that both elements are largely accommodated into accessory minerals and were not disturbed by alteration. The CV values of the different rock units show normal distribution, where all the percentages of CV values are less than 100, with the exception of eU of felsite that shows CV % value slightly higher than 100. The aplite‐pegmatite, alkali granite, and the associated pegmatite veins show negative value of uranium outward migration, but are still the most favorable host rocks for uranium and thorium mineralization. A tentative interpretation of such contradiction suggests that uranium is largely accommodated into accessory minerals and only limited labile uranium redistribution has occurred and uranium was precipitated in association with alteration products. This interpretation is supported by the presence of kasolite Pb(UO2)SiO4.(H2O), along the fractured zones and quartz veins in the aplite‐pegmatite. The limited uranium migration in the study area was also revealed by the low weathering rate estimated by the calculations of chemical indices of alteration.","PeriodicalId":21089,"journal":{"name":"Resource Geology","volume":"6 1","pages":"105 - 122"},"PeriodicalIF":1.4,"publicationDate":"2020-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90446316","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"ASTER mapping of gypsum deposits of Thumrait region of southern Oman","authors":"S. Rajendran, S. Nasir","doi":"10.1111/rge.12245","DOIUrl":"https://doi.org/10.1111/rge.12245","url":null,"abstract":"This study demonstrates the use of ASTER data for the mapping of gypsum deposits and associated geological formations that occurred in the Thumrait region of southern Oman. The measurement of spectra over samples of gypsum in the 1,300–2,500 nm wavelength using a PIMA spectrometer showed the presence of distinct absorptions at 1400–1600, 1750, 1940, 2,100, and 2,400 nm characteristics to OH stretching, H2O combinations, and SO bending overtones and stretching, respectively. Studying the unique spectral absorption characters of gypsum samples, we developed a false color composite (FCC) and an image by decorrelation stretch using the spectral bands 7, 3, and 2 of ASTER. The results FCC showed the regions of gypsum occurrences, and the decorrelated image discriminated the gypsum occurrences from other geological formations of the area. The study of surface mineralogy of the region using the VNIR‐SWIR bands by the spectral angle mapper method showed the presence of sulfate, carbonate, and clay minerals of the geological formations in the study area. We compared the results of ASTER with the results obtained using spectral bands 12, 8, and 4 of Sentinel‐2A processed by the same methods. The study showed that the spectral bands of ASTER can be used for mapping the gypsum and associated geological formations.","PeriodicalId":21089,"journal":{"name":"Resource Geology","volume":"118 1","pages":"41 - 62"},"PeriodicalIF":1.4,"publicationDate":"2020-12-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76143456","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Distribution of gold and silver and its relation with hypogene ore minerals in the Esperanza porphyry deposit, Antofagasta Region, Chile","authors":"S. Kojima, María Constanza San Martín, T. Nagase, D. Nakashima, C. Bisso, A. Menzies","doi":"10.1111/rge.12250","DOIUrl":"https://doi.org/10.1111/rge.12250","url":null,"abstract":"Modes of occurrence of Au‐ and Ag‐bearing phases and their relation with associated hypogene ore minerals were examined with the objective to elucidate Au‐Ag distribution at the Esperanza porphyry deposit in the Eocene Centinela copper belt, using ore‐microscope modal analysis, semi‐quantitative analyses by automated mineralogy, electron probe microanalysis, and secondary ion mass spectrometer. The Esperanza hypogene mineralization is characterized by early‐stage chalcopyrite‐rich veinlets in the potassic alteration zone and later polymetallic stage with tennantite and galena in the chlorite‐sericitic alteration zone. Only the early‐stage chalcopyrite contains fine‐grained electrum (Au68Ag32 ‐ Au81Ag19) and hessite (Ag2Te), and thus yields positive correlations in Cu vs. Au and Cu vs. Ag grades that are clearly recognized in the hypogene sulfide zone. The early‐stage chalcopyrite grains frequently exhibit polysynthetic twinning suggestive of inversion from intermediate solid solution. These features suggest that the fine‐grained electrum and hessite are products exsolved in the cooling process with the intermediate solid solution to chalcopyrite inversion. In contrast, tennantite and galena of the later‐stage mineralization contain no detectable Ag, and it is thus proposed that the early‐stage inverted chalcopyrite is the principal storage of economically important precious metals.","PeriodicalId":21089,"journal":{"name":"Resource Geology","volume":"13 1","pages":"80 - 90"},"PeriodicalIF":1.4,"publicationDate":"2020-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89313604","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Overprinting porphyry‐type veinlets on the intrusive rocks and phreatomagmatic breccias in the Southwest prospect, southwestern Sto. Tomas II (Philex), Baguio District, Philippines","authors":"Avriel Venis Literal Cirineo, A. Imai, R. Takahashi, Redempta P. Baluda, N. Oliveros, V. B. Maglambayan, Roy Ronald C. Luis, Maria Lourdes M. Faustino, Jacky P. Almadin","doi":"10.1111/rge.12242","DOIUrl":"https://doi.org/10.1111/rge.12242","url":null,"abstract":"The Southwest prospect is located at the southwestern periphery of the Sto. Tomas II porphyry copper–gold deposit in the Baguio District, northwestern Luzon, Philippines. The Southwest prospect hosts a copper‐gold mineralization related to a complex of porphyry intrusions, breccia facies, and overlapping porphyry‐type veinlets emplaced within the basement Pugo metavolcanics rocks and conglomerates of the Zigzag Formation. The occurrences of porphyry‐type veinlets and potassic alteration hosted in the complex are thought to be indications of the presence of blind porphyry deposits within the Sto. Tomas II vicinity. The complex is composed of at least four broadly mineralogically similar dioritic intrusive rocks that vary in texture and alteration type and intensity. These intrusions were accompanied with at least five breccia facies that were formed by the explosive brecciation, induced by the magmatic–hydrothermal processes and phreatomagmatic activities during the emplacement of the various intrusions. Hydrothermal alteration assemblages consisting of potassic, chlorite–magnetite, propylitic and sericite–chlorite alteration, and contemporaneous veinlet types were developed on the host rocks. Elevated copper and gold grades correspond to (a) chalcopyrite–bornite assemblage in the potassic alteration in the syn‐mineralization early‐mineralization diorite (EMD) and contemporaneous veinlets and (b) chalcopyrite‐rich mineralization associated with the chalcopyrite–magnetite–chlorite–actinolite±sericite veinlets contemporaneous with the chlorite–magnetite alteration. Erratic remarkable concentrations of gold were also present in the late‐mineralization Late Diorite (LD). High XMg of calcic amphiboles (&gt;0.60) in the intrusive rocks indicate that the magmas have been oxidizing since the early stages of crystallization, while a gap in the composition of Al between the rim and the cores of the calcic amphiboles in the EMD and LD indicate decompression at some point during the crystallization of these intrusive rocks. Fluid inclusion microthermometry suggests the trapping of immiscible fluids that formed the potassic alteration, associated ore mineralization, and sheeted quartz veinlets. The corresponding formation conditions of the shallower and deeper quartz veinlets were estimated at pressures of 50 and 30 MPa and temperatures of 554 and 436°C at depths of 1.9 and 1.1 km. Temperature data from the chlorite indicate that the chalcopyrite‐rich mineralization associated with the chlorite–magnetite alteration was formed at a much lower temperature (ca. 290°C) than the potassic alteration. Evidence from the vein offsetting matrix suggests multiple intrusions within the EMD, despite the K‐Ar ages of the potassic alteration in EMD and hornblende in the LD of about the same age at 3.5 ± 0.3 Ma. The K‐Ar age of the potassic alteration was likely to be thermally reset as a result of the overprinting hydrothermal alteration. The constrained K‐Ar ages also indicate","PeriodicalId":21089,"journal":{"name":"Resource Geology","volume":"12 1","pages":"1 - 40"},"PeriodicalIF":1.4,"publicationDate":"2020-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81962952","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}