Numerical Simulation Based Targeting of the Magushan Skarn Cu-Mo Deposit, Middle-Lower Yangtze Metallogenic Belt, China

The Magushan Cu–Mo deposit is a skarn deposit within the Nanling–Xuancheng mining district of the Middle-Lower Yangtze River Metallogenic Belt (MLYRMB), China. This study presents the results of a new numerical simulation that models the ore-forming processes that generated the Magushan deposit and enables the identification of unexplored areas that have significant exploration potential under areas covered by thick sedimentary sequences that cannot be easily explored using traditional methods. This study outlines the practical value of numerical simulation in determining the processes that operate during mineral deposit formation and how this knowledge can be used to enhance exploration targeting in areas of known mineralization. Our simulation also links multiple subdisciplines such as heat transfer, pressure, fluid flow, chemical reactions, and material migration. Our simulation allows the modeling of the formation and distribution of garnet, a gangue mineral commonly found within skarn deposits (including within the Magushan deposit). The modeled distribution of garnet matches the distribution of known mineralization as well as delineating areas that may well contain high garnet abundances within and around a concealed intrusion, indicating this area should be considered a prospective target during future mineral exploration. Overall, our study indicates that this type of numerical simulation-based approach to prospectivity modeling is both effective and economical and should be considered an additional tool for future mineral exploration to reduce exploration risks when targeting mineralization in areas with thick and unprospective sedimentary cover sequences

Application of Electron Probe Microanalyzer to Study the Textures and Compositions of Alteration Coronas of Monazite from the Longhuashan Granite, Northern Guangdong Province

BACKGROUND: Monazite is a common uranium-bearing accessory mineral in granite-related uranium deposits in South China. The Longhuashan pluton is an important U-bearing granite in the Zhuguangshan batholith, Northern Guangdong. Distinct alteration coronas of monazite were observed in the pluton. However, textures and compositions of alteration coronas of monazite and their implications for uranium mineralization are still poorly understood.OBJECTIVES: To investigate the detailed textural and compositional evolution of monazite in granites during alteration, and to provide insights into uranium mobilization and enrichment in granite-related uranium deposits.METHODS: Textures and chemical compositions of alteration coronas of monazite were investigated using electron probe microanalyzer (EPMA).RESULTS: Alteration coronas of monazite in the Longhuashan granite consisted of newly formed apatite, allanite, epidote, and Th-rich phases. The monazite alteration coronas area was a concentric zone composed of monazite, apatite (including thorium-rich minerals), and monazite-epidote from the inside to the outside. Mass balance calculations showed that during the alteration of monazite, light rare earth (LREE), Y, Th, and U elements were remobilized and migrated, and the fluid brought in elements such as Ca, Fe, Al, and F to form alteration coronas composed of apatite, epidote, and thorium-rich minerals. The EPMA mapping showed that monazite alteration led to the remobilization of uranium, but the uranium was mainly enriched in the altered coronas. In this pluton, 3.7% U was located in monazite, and more than 80% U was hosted by uraninite.CONCLUSIONS: Monazite only contributes limited uranium to regional uranium mineralization, and uraninite is the most important host for uranium in the Longhuashan granite

Geochemical studies on Permian manganese deposits in Guichi, eastern China: Implications for their origin and formative environments

Permian manganese ore deposits are widely distributed in southwestern and eastern China. Guichi Permian manganese district in southern Anhui Province, central eastern China, is currently the most important manganese metal producers in eastern China. Manganese ores (MnO = 18.2-45.4 wt.%) in Guichi region occur in calcareous, argillaceous and siliceous Mn-bearing sequence of the Permian Gufeng Formation. In contrast to Mn-bearing rocks, the ores have higher Mn, Fe, P, Sr (more than 1500 ppm) and Ni contents (>480 ppm), higher Mn/Fe (>5) and La-n/Ce-n (>2) values, and lower Co/Ni (<0.05) ratios. The Guichi manganese deposits also have low Co/Ni (<1) and Co/Zn ratios, low in total REE contents (mostly < 100 ppm) with negative Eu (0.46-0.75) and Ce (0.42-0.76) anomalies. The mineralogy and geochemistry of manganese deposits in the Guichi region strongly indicate hydrothermal activities, which is supported by high paleotemperatures (49-71 degrees C) of Permian Mn-carbonate ore and Mn-bearing carbonate. The low Ce-anom. values (<-0.1) and high strontium contents indicate that the Guichi manganese deposits were formed in high-salinity and oxidative marine sedimentary environment. The Al2O3/TiO2 (9.23-48.2) and Y/Ho (25.9-44.4) ratios, REE patterns, delta C-13(V-PDB) (-10.2 parts per thousand to 5.00 parts per thousand) and delta O-18(SMOW) (20.7-28.0 parts per thousand characteristics of Permian manganese deposits reveal a mixed Mn source of volcanic, terrigenous and organic matter. (C) 2013 Elsevier Ltd. All rights reserved

Geochemical characteristics and tectonic setting of the Tuerkubantao mafic-ultramafic intrusion in West Junggar, Xinjiang, China

Mineral chemistry, whole-rock major oxide, and trace element compositions have been determined for the Tuerkubantao mafic-ultramafic intrusion, in order to understand the early Paleozoic tectonic evolution of the West Junggar orogenic belt at the southern margin of the Central Asian orogenic belt. The Tuerkubantao mafic-ultramafic intrusion is a well-differentiated complex comprising peridotite, olivine pyroxenite, gabbro, and diorite. The ultramafic rocks are mostly seen in the central part of the intrusion and surrounded by mafic rocks. The Tuerkubantao intrusive rocks are characterized by enrichment of large ion lithophile elements and depleted high field strength elements relative to N-MORB. In addition, the Tuerkubantao intrusion displays relatively low Th/U and Nb/U (1.13–2.98 and 2.53–7.02, respectively) and high La/Nb and Ba/Nb (1.15–4.19 and 37.7–79.82, respectively). These features indicate that the primary magma of the intrusion was derived from partial melting of a previously metasomatized mantle source in a subduction setting. The trace element patterns of peridotites, gabbros, and diorite in the Tuerkubantao intrusion have sub-parallel trends, suggesting that the different rock types are related to each other by differentiation of the same primary magma. The intrusive contact between peridotite and gabbro clearly suggest that the Tuerkubantao is not a fragment of an ophiolite. However, the Tuerkubantao intrusion displays many similarities with Alaskan-type mafic-ultramafic intrusions along major sutures of Phanerozoic orogenic belts. Common features include their geodynamic setting, internal lithological zoning, and geochemistry. The striking similarities indicate that the middle Devonian Tuerkubantao intrusion likely formed in a subduction-related setting similar to that of the Alaskan-type intrusions. In combination with the Devonian magmatism and porphyry mineralization, we propose that subduction of the oceanic slab has widely existed in the expansive oceans during the Devonian around the Junggar block

Hydrothermal fluid characteristics and implications of the Makou IOA deposit in Luzong Basin, eastern China

A large number of iron oxide–apatite (IOA) deposits occur in the Middle and Lower Yangtze River metallogenic belt (MLYB), eastern China. Proterozoic phosphorus-rich strata are also widely exposed in this belt, providing a good opportunity to research the relationship between phosphorus-rich layers and IOA deposits. The Makou IOA deposit is located in the central part of the volcanic Luzong Basin. The ore body is developed in the contact zone between gabbro-diorite and Cretaceous trachyandesite, and it is the only IOA deposit in the basin that spatially associated with a dioritic intrusion. The main hydrothermal alteration minerals are albite, diopside, apatite, chlorite, and carbonate. In this study, we employed SHRIMP SI to analyse in situ O isotope ratios of magmatic and hydrothermal apatite and in situ S isotope ratios of pyrite from the Makou deposit. Additionally, LA-ICP-MS was used for trace element analysis. The results show that the sulfur in the pyrite of the Makou deposit comes from different sulfur phases (e.g. H2S and SO2) in the hydrothermal fluid, and ΣS34total is similar to that of magmatic sulfur, indicating that the hydrothermal fluid was weakly affected by evaporite, which is substantially different from other IOA/skarn iron deposits in the MLYB. Both analysed apatite samples are classified as fluorapatite, in which the δ18Oap of the Makou magmatic/hydrothermal apatite is similar to that of the initial mantle (3.7–5.5‰) and much lower than that of the Susong sedimentary-metasomatic apatite (13.7–14.2‰). The LREE/HREE ratio increase from magmatic to hydrothermal apatite, whereas the Sr/Y decreases, indicating that the hydrothermal fluid metasomatised the dioritic intrusive rock, resulting in a large amount of albite crystallisation and release Fe from pyroxene and biotite to hydrothermal fluid, indicates that Fe-rich fluid in IOA deposit could be formed by albitization of the consolidated intrusive rock. By combining this finding with the oxygen isotope data, we propose that the mineralization of the Makou deposit was mainly controlled by a magmatic-hydrothermal process. The low CO2 and SO42− contents in the volcanic rock are a key factor leading to apatite precipitation. The addition of a phosphorus-rich layer or evaporites is not necessary for the formation of IOA-type deposits in the MLYB.This work was financially supported by the National Natural Science Foundation of China (grant nos. 41672081, 41320104003, 41172086), the National Key Research and Development Plan (grant no. 2016YFC0600206) and the Fundamental Research Funds for the Central Universities of China (grant no. JZ2020HGQB0227, PA2019GDZC0093

Petrogenesis and metallogenic implications for the Machang, Huangdaoshan, and Tuncang plutons in eastern Anhui: an integrated age, petrologic, and geochemical study

<p>The Tuncang–Chuzhou–Machang area (eastern Anhui province) is geologically located in the intersection between the Yangtze block and the Qinling–Dabie orogenic belt. Many Mesozoic plutons outcrop in this district that are Cu–Au prospective but inadequately studied. We report new LA-ICP-MS zircon U–Pb ages, petrologic, and whole rock geochemical data for three representative plutons at Machang, Huangdaoshan, and Tuncang. New dating results suggest that all the Machang (129.3 ± 1.6 Ma), Huangdaoshan (129 ± 1.7 Ma), and Tuncang (130.8 ± 1.9 Ma) plutons were emplaced in the Early Cretaceous, slightly older than other plutons in neighbourhood of the Zhangbaling uplift. The three plutons contain typical low-Mg adakitic affinities, in which the rocks contain SiO₂ >56%, Al₂O₃ ≥15%, Mg# <53, elevated Sr, Ba, Cr, Ni, Sr/Y, and La/Yb, low Y and Yb and no discernible Eu anomaly. Their petrogenesis may have been related to the delamination and partial melting of the lower crust, which is different from the Chuzhou pluton, which was interpreted to have formed by partial melting of the subducted slabs. We suggest that this petrogenetic difference may explain why the pluton at Chuzhou is Cu–Au fertile, whereas those at Machang, Huangdaoshan, and Tuncang are largely barren. It is proposed that adakitic plutons formed by partial melting of the subducted slabs have high metallogenetic potentiality in the area.</p

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

The Chating deposit is a porphyry copper deposit in the Middle Lower Yangtze River Valley Metallogenic Belt, with skarns found in both the carbonate wall rock and in carbonate xenoliths in the intrusions. Detailed drill hole logging identified endoskarn and exoskarn in Chating, mainly distributed inside the ore–bearing quartz diorite porphyry instead of at the contact with the country rock. The skarns at Chating are unmineralized unless overprinted by porphyry related copper mineralization. Garnet in the Chating skarns can be divided into several types based on their occurrence and whether they were overprinted by porphyry mineralization. The garnets from the ore–bearing (G1a), barren endoskarn (G1b) and proximal ore–bearing exoskarn (G2a) are LREE-enriched, HREE–depleted with positive Eu anomalies whereas garnets from the barren massive exoskarn (G2b) are LREE-enriched with flat HREE and negative Eu anomalies. The G3 garnets are from marbleized skarn distal to the ore-bearing quartz diorite porphyry and consist of Al-rich and Fe-rich andradite; the Al–rich G3 garnets are LREE-depleted and HREE-enriched whereas the Fe-rich G3 garnets are LREE-enriched and HREE-depleted, both have negative Eu anomalies. The physicochemical conditions and composition of skarn-forming fluids controlled the REE, Eu, U and Y distribution in the garnets. The similarities of the REE patterns to those of magmatic–derived fluids suggests a dominantly magmatic fluid formed the endoskarn and proximal exoskarn. Fluid–rock interaction and addition of external fluids diluted the fluid that formed the exoskarn, decreasing the Cl and metal contents, resulting in lower REE contents and negative Eu anomalies in G2b and G3 garnets. The δ S data for anhydrite from potassic alteration, sericite alteration, endoskarn and exoskarn range from 3.51‰ to 10.92‰, consistent with a dominantly magmatic fluid source. The δ S for the anhydrite from the skarns ranges from 3.51‰ to 8.74‰, which combined with the absence of coeval sulfides, suggests a very high oxygen fugacity for the skarn-forming fluids. The small-scale skarns in Chating contain more anhydrite than garnet and consequently did not act as ground preparation as they do in typical skarn deposits. We propose that the anhydrite-rich exoskarn and the small scale of the endoskarn, combined with the high oxygen fugacity and low Cl content in the skarn-forming fluids resulted in the barren skarns of the Chating deposit. 34 34This work was financially supported by the National Key Research and Development Program of China (2016YFC0600206), the Natural Science Foundation of China (grants 41320104003, 91962218), the Fundamental Research Funds for the Central Universities of China (grants PA2019GDZC0093) and the China Scholarship Council (CSC) (201906690031), the National Natural Science Foundation of China (grant no. 41702071), and the Academic newcomer promotion plan B of Hefei University of technology (JZ2019HGTB0070)

Magma generation and sulfide saturation of Permian mafic-ultramafic intrusions from the western part of the Northern Tianshan in NW China: implications for Ni-Cu mineralization

Compared to Permian magmatic Ni-Cu sulfide deposits in the eastern part of the Northern Tianshan, such as Huangshan and Huangshandong, those in the western part (e.g., Baixintan and Lubei) are poorly documented. Zircon ID-TIMS U-Pb age data (279.7 ± 0.2 Ma) of lherzolite and LA-ICPMS U-Pb age data (277.8 ± 3.4 Ma) of a hornblende gabbro suggest the Lubei intrusion was emplaced in the Early Permian. The Baixintan and Lubei mafic-ultramafic intrusive rocks are characterized by enrichments of large ion lithophile elements and Th and U relative to the high field strength elements, as well as depletion of Nb and Ta relative to mid-ocean ridge basalt. The (87Sr/86Sr)t (0.70354–0.70713), εNd(t) (2.80 to + 7.05), and εHf(t) (2.50–18.4) values for the intrusions indicate that they have assimilated Tianshan basement rocks, whereas the Se/S ratios (181 × 10−6 –418 × 10−6 ) and δ34SCDT values (− 0.13‰ to 0.90‰) of the sulfides suggest that crustal sulfur has not been incorporated into the magma. The decrease in Pd/Zr with increasing (Th/Nb)PM indicates that sulfide saturation accompanied crustal contamination. The olivine compositions and whole-rock chalcophile elements of the Baixintan and Lubei intrusions imply that the parental magma of the intrusive rocks in the west contains higher chalcophile elements than those in the east, which suggests that the mafic-ultramafic intrusions in the western part of the Northern Tianshan should be regarded as favorable Ni-Cu sulfide exploration targets.This work was supported by the National Natural Science Foundation of China (Grant Nos. U1803113, 41672069, 41630316, 41303031, and 41820104007), the China Academy of Science BLight of West China^ Program, and the Fundamental Research Funds for the Central Universities (JZ2018HGTB0246)

Ore-fluid geochemistry of the Hehuashan Pb–Zn deposit in the Tongling ore district, Anhui province, China: evidence from REE and C–H–O isotopes of calcite

Calcite is the main gangue mineral of the Hehuashan lead–zinc deposit, which is located in the Tongling ore district, Anhui Province, East China. The ore bodies of the Hehuashan deposit are hosted by dissolution breccia of the Lower Triassic carbonate sediments. We report petrography, rare earth elements (REE), and C–H–O isotope data of four generations of calcite recognized in the Hehuashan deposit, namely the pre-ore stage calcite (Cal-1), early ore-forming stage calcite (Cal-2), late ore-forming stage calcite (Cal-3) and post-ore stage calcite (Cal-4). In addition, we also report C–H–O isotopes data of dolostone from the Lower Triassic carbonate sediments. All four calcite generations show a low ∑REE content (13–50 ppm on average), indicating that the related ore-forming fluids may not have been derived a magmatic fluid but rather be derived from the carbonate sediments or basinal brines. Low LREE/HREE ratio (1.1–6.1 on average) of all four calcite generations implies that no significant REE fractionation happened during the mineralizing processes. The wide distribution of Y/Ho ratios (17–70) of calcite indicates a result of fluids mixing. The δ¹³C values of calcite (1.4‰ to 4.2‰) are comparable to marine carbonates, but the δ¹⁸O values are lower, indicating possibly a result of carbonates dissolution. Calculated δ¹⁸O of the fluid in equilibrium with calcite vary from –3.1‰ to –0.1‰, combining the δDV-SMOW (–100‰ to –81‰), implying a fluid mixing of a brine fluid and meteoric water or diagenetic pore water for the mineralization of the Hehuashan deposit