Wall Rocks Research Articles

Mantle-like to low oxygen isotopes in zircon from the mid-Cretaceous high-silica granites reveal unweathered basement recycling along the present coastal area of SE China

Zircon oxygen isotope compositions can provide potential constraints on the origin of granitic magmas. In this work, we report new data of zircon UPb dating, trace elements and HfO isotopes for two types of mid-Cretaceous high-silica granites from Zhoushan archipelago in Zhejiang Province, SE China. The in-situ zircon data are carefully screened for radiation damage and post-magmatic alteration. The analyzed magmatic zircon grains indicate that the Zhoushan calc-alkaline granites (ZCAG; 101–92 Ma) have mantle-like δ18O values of 5.29–5.88 ‰, in contrast to the Zhoushan peralkaline granites (ZPAG; 91–89 Ma) with relatively low δ18O of 4.42–4.6 ‰. The slight decreases in δ18O and εHf(t) from zircon center to periphery of both groups suggest that they may have consistent oxygen isotopic compositions in their parental magma sources and have gone through assimilations to hydrothermally altered wall rocks in the shallow crust. The mantle-like δ18O values in zircon are widespread in the Cretaceous felsic rocks in the present coastal area of SE China, which, in combination Hf isotopes, indicates the possible existence of a buried unweathered Proterozoic basement in the eastern part of the Cathaysia Block. This work highlights the role of deep crustal magma sources, assimilation and post-magmatic radioactive damage on the formation of mantle-like to low δ18O signals in zircons, and has fundamental implications for understanding the formation of widespread mid-Cretaceous felsic rocks along the present coastal area of SE China.

Geochemistry and geochronology of Beiya giant Au polymetallic deposit: Implications for multistage ore-fluid pulses in a skarn system

Garnet is one of the most typical minerals in skarn deposits, and its texture and composition is a proxy for the changing physicochemical conditions. Thus, mineralogical and geochemical characterization of different garnet types can provide important information on the nature and evolution of ore-forming fluids. The Beiya gold-polymetallic deposit is China’s largest skarn-type Au deposit with Au reserves of >380 t. Although several studies have addressed the skarn formation mechanism and nature of fluid evolution, a systematic study on the changes in the composition and texture of garnet from wall rocks to ore-related intrusion has not yet been attempted. In this work, we carry out a systematic investigation along a horizonal profile in the open pit of the Beiya deposit. Our results show that the garnet in the profile belongs to grossular-andradite solid solution series with all grains showing well-developed fine oscillatory zoning. The garnets are of two types: the first type (Grt I) formed within the endoskarn, is reddish to red with euhedral-subhedral megacryst structure (>10 mm) and has altered surfaces. The second type (Grt II) occur in the proximal exoskarn, is red to brown–red, euhedral-subhedral, with medium- to fine- grained structure (0.3–4 mm) and displaying oscillatory zoning. Unlike Grt I, hydrous minerals occur in the pores among Grt II garnets, such as calcite, quartz, epidote and chlorite. Also, calcite-chlorite vein, quartz vein and quartz-chalcopyrite-pyrite vein cuts the Grt II garnets. Grt I is dominantly grossular (Adr14.88-43.58Grs55.25-82.87), depleted in the large ion lithophile elements (LILE), relatively enriched in high field strength elements (HFSEs) and enriched in heavy rare earth elements (HREEs) with negative Eu anomalies. Grt II is mostly andradite (Adr62.18-98.91Grs0-36.22), depleted in the LILE and HFSE, enriched in light rare earth elements (LREEs) with slightly positive Eu anomalies. Here we selected Grt II for in-situ LA-ICP-MS U-Pb dating, since Grt I contains negligible uranium. The results yielded a lower intercept 206Pb/238U age of 35.3 ± 1.8 Ma (MSWD = 0.68, n = 23). The calculated oxygen isotopic compositions of hydrothermal fluids in equilibrium with two types of garnets range from 6.46 ‰ to 8.56 ‰ (average 7.89 ‰), which are within the range of values for magmatic fluids. We infer that the physicochemical conditions of the hydrothermal fluid changed from relatively reduced, nearly neutral, and low water/rock ratios to slightly oxidized, slightly acidic, and high water/rock ratios. The chlorine content in the fluid increased during garnet growth. The fluctuating compositions of garnets in the skarn suggest multistage ore-fluid activities and the fluid evolution provide insights into the ore-forming process.

Source and genesis of Chapai carbonate-hosted Zn-Pb deposit, South China: Constraints from in-situ S and Pb isotopes of sulfide and sulfate minerals

Chapai deposit is a special medium-sized carbonate-hosted Zn-Pb deposit (4.27Mt of sulfide ore with 8.15 % Zn, 3.44 % Pb, and 53.39 g/t Ag, as well as 0.82Mt of oxidized ore with 2.8 % Zn and 1.2 % Pb and 27.68 g/t Ag) with upper oxidized ore and lower sulfide ore of South China. Due to the shortage of detailed geological and geochemical constraints, the ore genesis of single stage magmatic hydrothermal mineralization or superposition of multi-stage mineralization remains unclear. Therefore, detailed geological and geochemical analyses of in-situ S isotopic compositions of sulfide and sulfate, trace elements of sphalerite, and ore Pb isotopic compositions were performed to decode the source and genesis of the Chapai deposit. Based on the investigation and microscopic observation, mineralization of the Chapai Zn–Pb deposit has obvious early hydrothermal alternation in the early hydrothermal sulfide stage (S1) and the late hydrothermal sulfide stage (S2) as well as the supergene oxidized mineralization stage (S3). The trace elements Cu, Ag, Ga, Sb, As and Ge are incorporated into S1 and S2 stages of sphalerite mainly through the following substitution mechanisms: Zn2+↔ (Fe2+, Cd2+),2Zn2+↔ (Ag+, Cu+) +(As3+, Ga3+, Sb3+), 3Zn2+↔ Ge4++2(Cu++Ag+), 4Zn2+↔(Cu++Ag+) + Sb3++Ge4++□(vacancy). In situ δ34S values of sulfides and sulfates are within a greater range (–3.0 to + 32.2 ‰), and are significantly higher in S2 compared to S1 stage, implying the mixing of two isotopically different end-members of hydrothermal fluids and wall rocks by sulfate reduction. The S isotope of sphalerite and galena crystallized in the early stage close to 0 ‰ may be controlled by magmatic-hydrothermal fluid source, while the increased S isotope in the late stage may be derived from the increased decomposition of organic matter and organic sulfate reduction (TSR). The Pb isotopic data (206Pb/204Pb = 18.355 ∼ 18.819, 207Pb/204Pb = 15.720 ∼ 15.778, and 208Pb/204Pb = 38.912 ∼ 39.222) indicate that the sources of metallogenic materials in the Chapai deposit are primarily upper crust basement rocks. The geothermometer studies of sphalerite in Chapai deposit show that it was generated from a medium–low temperature (142 ∼ 255 °C) condition. The low Zn/Cd ratios and high concentrations of Cd and Ge in sphalerite are in agreement with those of Mississippi Valley-type (MVT) deposits. Hence, the Chapai deposit was formed in a medium–low temperature magmatic- hydrothermal system and can be categorized as a MVT deposit within Nanling region (NR).

Ascent and emplacement controls of mafic magmas in the mid crust − evidence from 3D modelling of basic bodies of the Koperberg Suite, Namaqualand

Abstract The 3D modelling of basic bodies of the Koperberg Suite (1060 to 1030 Ma) and their wall rocks from Narrap Mine illustrates the distribution, geometries and, by implication, processes that determined the ascent and emplacement of the mantle-derived mafic magmas into the partially-molten, mid-crustal granite-gneiss sequence of the Okiep Copper District in Namaqualand. The lens-like, discontinuous geometry of basic bodies suggests the transfer of the mafic magmas as self-contained, buoyancy-driven hydrofractures. The presence of both shallowly-dipping, foliation-parallel sills and subvertical lenses in zones of steep foliation development, so-called steep structures, indicates an emplacement of the mafic magmas under low deviatoric stresses and irrespective of the regional stress field. Instead, the emplacement of the mafic magmas parallel to pre-existing anisotropies (tectonic fabrics or lithological contacts) highlights those differences in tensile strength and fracture toughness parallel to or across anisotropies determined the propagation of the magmas. This also accounts for the common occurrence of basic bodies in steep structures in which the vertical gneissosity promoted the buoyancy-driven ascent of the mafic magmas. On a regional scale, the mechanical stratification of the subhorizontal, sheet-like granite gneisses and interlayered metasediments exerted important controls on the ascent of Koperberg Suite magmas. The preferential emplacement of basic bodies in schist and gneiss units suggests that the lower rigidity of the ductile wall rocks facilitated magma emplacement through a combination of viscous wall-rock deformation and fracture blunting that led to the arrest of the magma-filled hydrofractures. Multiple intrusive relationships of successively emplaced magma batches suggest that later magmas reutilised earlier established magma pathways, particularly in steep structures. High-rigidity lithologies, such as the massive Springbok Quartzite, in contrast, only allowed for smaller fracture apertures and limited dilation, resulting in the pinching of basic bodies and rather stringer-like geometries. It is conceivable that the higher fracture toughness of the quartzite may also have prevented propagation of the mafic magmas through the Springbok Quartzite and, instead, led to the ponding of basic bodies below the metasediments. The geometry and structural and lithological controls of basic bodies at Narrap Mine are similar to Koperberg Suite intrusions documented from many of the other mine workings in the Okiep Copper District. This suggests similar underlying emplacement controls of the cupriferous rocks, which can be extrapolated on a regional scale and that may guide exploration.

Petrogenesis of the Wushi carbonatites in the northwestern Tarim Basin: Implications to deep carbon recycling

Carbonatites are rarely exposed on the Earth's surface, and most of them are supposed to have been mantle-derived. However, in the most recent years, carbonatites with pronounced crustal signatures had also been recognized. Although carbonatites have attracted the attention of many researchers, their genesis remains controversial. In this study, we present a systematic C–O–Sr–Nd–Mg isotopic investigation on the carbonatites exposed in Wushi County located at the northwestern margin of the Tarim Basin to determine their petrogenesis. The Wushi carbonatites, containing the xenoliths of wall rocks, intruded into Precambrian sandstones as dykes. Carbonatites predominantly comprise calcite and accessory minerals, such as dolomite, apatite, mica and quartz, and thus are classified as calciocarbonatites. Trace element geochemistry indicates that the total rare earth element (REE) concentrations in Wushi carbonatites range from 13.6 to 57.3 ppm, with an average of 30.9 ppm. The chondrite-normalized REE patterns of the test samples indicate that light rare earth elements (LREE) in the samples have been enriched relative to their heavy rare earth elements (HREE) and that the LREE/HREE ratios vary from 6.0 to 9.1. The patterns also show negative Eu anomalies (δEu = 0.65–0.75) and weak negative Ce anomalies (δCe = 0.75–0.99). The primitive mantle-normalized trace element spider diagrams display the enrichment of large ion lithophile elements (LILE), such as Pb, Sr and Ba, and the strong depletion of high field strength elements (HFSE), such as Nb, Ta, Zr, Hf and Ti. The δ18OV-SMOW (15.9‰–18.2‰) and δ13CV-PDB (−2.97‰–3.36‰) values are more consistent with those of crust-derived carbonatites than with mantle-derived carbonatites. The values of δ18OV-SMOW and δ13CV-PDB are consistent with the high values of 87Sr/86Sr (0.7096–0.7110) and low values of 143Nd/144Nd (0.5118–0.5120). Typically, δ26Mg of the carbonatites (−1.76‰ to −1.27‰) is much lighter than the δ26Mg of the mantle (−0.25‰ ± 0.04‰) but heavier than the δ26Mg of sedimentary carbonates (−2.72‰ to −2.15‰) obtained from the neighbouring Western Tianshan orogenic belt. The light Mg isotope anomalies cannot be explained using secondary alteration, continental crustal contamination, kinetic isotope fractionation and fractional crystallization. Thus, these anomalies could be due to the isotope exchange reactions occurring between the oceanic crust and sedimentary carbonates during subduction. In this study, we propose a two-stage model to explain Wushi carbonatite formation based on its isotope characteristics. During the early stage of carbonatite formation, sedimentary carbonate rocks located along the northern margin of the Tarim Craton and oceanic crust were subducted into the deep mantle. Isotope exchange and carbonation occurred during subduction to form carbonated eclogite. In the second stage of carbonatite formation, the heat produced by the Permian mantle plume in the Tarim Basin melted the carbonated eclogite to produce carbonatite melt. Thus, the petrogenesis of the Wushi carbonatites revealed by the presence of multiple isotopes indicates that the carbonatite produced by carbonated eclogite in the deep mantle would exhibit typical crustal isotopic characteristics and provide new insights into deep carbon recycling.

Apatite Geochemical and Nd Isotopic Insights into Trachyte Petrogenesis in the Tianchi Volcanic Area of Changbai Mountain, NE China

AbstractWe report the oxide, element geochemistry and Nd isotopic geochemical data of apatite in the middle Pleistocene medium‐ and fine‐grained trachyte in the Tianchi volcanic area (TVA) of Changbai Mountain, discussing the relationship between apatite and the composition of the whole rock. The purpose is to use the apatite geochemical data to constrain the evolutionary process of trachytic magma and the petrogenesis of trachyte in the cone‐forming period of the Tianchi volcano. Apatite (Ca5(PO4)3(OH, F, Cl)) is a common accessory mineral that occurs widely in volcanic rocks in the TVA. The apatites in the trachyte are mainly subhedral–anhedral, having the characteristics of magmatic apatite. In terms of oxide and element geochemistry, they have homogeneous Al2O3, SiO2, MgO, P2O5, K2O, CaO and heterogeneous TiO2, with high F content. They are generally enriched in Th, U and LREEs, depleted in Nb, Ta, Zr, Hf and HFSEs, showing negative Ba, Sr and Ti anomalies, similar to those of the whole‐rock host trachytes. The ratios of high (La/Yb)N, low δEu (Eu/Eu*), Sr/Y value and ΣREE content in apatite, and the F, Sr, Y, Th/U, La/Sm, and Nd/Tb with ΣREE and δEu anomalies showed a linear correlation, all of those indicating that the host magma has the characteristic of high differentiation. The apatite grains generally having 147Sm/144Nd, 143Nd/144Nd ratios and εNd(t) values of 0.1072–0.1195, 0.5123–0.5126 and –3.49 to –0.10, respectively, are similiar to those of the host rock. The Nd model ages TDM1 are 949–803 Ma in apatite. Combined with the εNd(t) value of the apatite core (–7.06 to –3.49), we conclude that the initial magma of the host trachyte was derived from the partial melting of Proterozoic crustal material and there was an assimilation of wall rocks during its evolution.

A Study on the Geological Characteristics and Metallogenic Laws of the Xilahe Copper Deposit in Yuanjiang County

The Xilahe copper deposit in Yuanjiang County, Yunnan Province, China, is a highly concerned copper mining area. The geological characteristics, structural characteristics, distribution of magmatic rocks, ore body characteristics, metamorphism and wall rock alteration, as well as the ore-forming horizon and mineralization characteristics of the deposit are described and analyzed in this article, revealing its mineralization laws. The strata of the ore deposit is mainly composed of the upper section of the Fei weihe Formation, and the structural characteristics show the development of multiple faults in the mining area, including magmatic rocks such as diabase. The characteristics of the ore body indicate the presence of five copper ore bodies, mainly sulfide ore, and the main metal mineral is Fool's Gold. Metamorphism and wall rock alteration are manifested as silicification, carbonization, and pyritization. The mineralization pattern is influenced by various geological factors, including geological structure, magnetic action, hydrothermal activity, and time factors. The deposit belongs to a sedimentary metamorphic copper deposit. Comprehensive analysis shows that the copper deposits in the study area have great potential for ore exploration, which has important theoretical and practical significance for subsequent exploration and application of ore exploration methods.

Contribution discrepancy of two distinct wall rocks to wolframite mineralization from Dongshanwan quartz-vein tungsten deposit, Southern Great Xing’an Range, China

The Southern Great Xing’an Range is a significant polymetallic metallogenic belt in Northeast China. The ages of granite related to tungsten mineralization have been well quantified, however, the timing and mechanism of quartz vein-type wolframite deposition remain unclear. Therefore, our study focused on the Dongshanwan tungsten deposit, representing a typical wolframite-bearing quartz vein-type deposit in the Southern Great Xing’an Range. Quartz vein-type tungsten mineralization was mainly contained in the Early Cretaceous granite porphyry, with few exceptions in the Permian tuff. Representative wolframite samples were collected from intragranitic (Wol-I) and intra-tuff (Wol-II) quartz veins for wolframite U–Pb dating, electron probe microanalysis (EPMA), and trace elemental analysis. Wolframite U–Pb dating recognized an Early Cretaceous mineralization event at 139–141 Ma, consistent with the previous Dongshanwan granite’s ages (∼142 Ma) but much younger than tuff (∼260 Ma). All the wolframite samples belonged to the ferberite series (FeO/MnO = 4.0–6.9), which indicates a link to the highly fractionated granite. Wol-I showed high contents of Nb, Ta, Sc, and HREEs and a strongly negative Eu anomaly (0.02–0.29), while these elements in Wol-II were approximately one order of magnitude lower than in Wol-I and the Eu anomaly was highly variable (0.17–1.02). The redox characteristics reflected by the Eu anomaly of wolframite may correspond to the variations in oxygen fugacity. Based on petrology, geochemistry, and element mass migration, this study suggests that the granite porphyry and tuff in the Dongshanwan deposit contributed differently to the wolframite precipitation even if the ore-forming fluids were of a common magmatic-hydrothermal origin. The exsolved fluid reserved in the closed system interacts with granite to achieve continuous enrichment in Nb, Ta, Sn, and REEs and accepts external Fe supply from granite alteration to precipitate Wol-I. In contrast, the fluids in relatively open and non-granitic systems have lower Nb, Ta, Sn, and REEs than the former, and Fe supply depends on the alteration of tuff. The abundance of fluorite and the non-CHARAC (CHArge-and-RAdius-Controlled) behavior of Y/Ho and Zr/Hf in the wolframite suggested that fluorine plays an important role in the migration and enrichment of tungsten and other elements during tungsten mineralization.

Genesis of the Shirengou gold deposit, northern North China Craton, based on zircon U[sbnd]Pb, fluid inclusion, sulfide compositional and S isotope data

The newly discovered vein-type Shirengou gold deposit on the northern edge of the North China Craton contains at least 8.69 tons of Au at an average grade of 9.80 g/t. Six auriferous quartz veins have been identified within Upper Jurassic rhyolitic breccia-bearing crystal-lithic tuff, and they follow NW-trending secondary faults. Gold mineralization was closely related to silicification, with pyrite as the predominant ore mineral. Four mineralization stages can be discerned, involving Stage I milky quartz, Stage II quartz-pyrite, Stage III gray quartz-polymetallic sulfide, and Stage IV quartz-calcite ± pyrite. Zircon UPb dating of a pre-ore porphyryritic rhyolite dike sets an upper age limit on the gold mineralization of ~131.1 Ma. Two-phase and single-phase aqueous inclusions were observed in quartz related to all four mineralization stages. From Stage I to Stage IV, the fluid inclusion homogenization temperatures decrease from respectively 257–340 °C to 230–277 °C, 201–250 °C and 161–200 °C, with corresponding salinities of 3.39–9.21, 2.24–8.00, 1.22–7.59, and 0.18–3.55 wt% NaCl equivalent, respectively. Thus, the ore-forming fluid can be described as moderate-high temperature, moderate-low salinity H2O-NaCl fluids. The δ34S values of sulfides vary from 0.0 to 5.3 ‰, indicating that the S was derived primarily from magmatic source(s), with some contribution from the metamorphic rocks of the surrounding Jianping Group. In-situ LA-ICP-MS trace element analysis of sulfides, together with our new age data, suggest that the ore-forming fluid was initially of Early Cretaceous magmatic-hydrothermal origin, and subsequently modified by interaction with the wall rocks of the Jianping Group, extracting the ore-forming metals from these rocks into the fluids.

Cobalt mineralization in the Northeastern Hunan Province of South China: New evidence from the Jintang hydrothermal Co polymetallic ore district

The hydrothermal vein-hosted Co deposits as one of the significant deposit types, have economic importance in the world. The Jiangnan Orogen of South China hosts abundant hydrothermal Co deposits, of which several Co (-polymetallic) deposits cluster together along the Changsha-Pingjiang fault zone in the northeastern Hunan Province. However, the variations of cobaltiferous mineral assemblages exhibit along the Changsha-Pingjiang fault zone. The Jintang ore district as the new prospecting target could provide an insight into the understanding of Co mineralization in the northeastern Hunan Province. The TIMA and EPMA results identify pyrite, arsenopyrite and minor cobaltite and glaucodot as the main cobaltiferous sulfide phases in the Jintang district, of which Co and Ni occur via substituting Fe in pyrite and arsenopyrite. In contrast with the barren pyrite (PyI) associated with marcasite in the early stage, the PyII of the middle stage is featured by the successive precipitation of Co-rich PyII-a (Avg. 2.93 wt%, up to 5.05 wt% Co), Ni-rich PyII-b (Avg. 1.56 wt%, up to 3.84 wt% Ni) and As-rich PyII-c (Avg. 1.36 wt%, up to 4.10 wt% As). The sharp chemical gradients across the different pyrite species as well as irregular reaction fronts indicate fluid-mediated dissolution and reprecipitation are principal mechanism for the incorporation of Co, Ni and As into sulfides. The fractionation of Co and Ni in pyrite was possibly caused by the decreasing salinity which favors high Ni/Co ratios in pyrite, rather than different fluid origins. Successively, the As-rich PyII-c together with arsenopyrite and glaucodot were precipitated, indicating a progressive increase of As concentrations in fluids and decreasing fO2 condition. The sulfur isotopic analyses yield the δ34SV-CDT values of −8.0 to −4.9 ‰ for the Jintang sulfides, suggesting both magma and wall rock as potential sulfur reservoirs. In combination with S and Pb isotopic results in this area, the Co mineralization in the northeastern Hunan Province was most likely formed via fluid-rock interactions along cataclastic fault zones with metal leached from the crystalline basement. The migration of ore-forming fluids along the Changsha-Pingjiang fault zone potentially contributed to the development of contrasting cobaltiferous mineral assemblages in the region, but the changes in local physicochemical conditions generated the partitioning of elements within a single deposit.

Magma-related origin for Pb–Zn–Ag vein formation at the Aerhada deposit, Inner Mongolia, NE China: Constraints from fluid inclusion, C–H–O–S–Pb isotopic compositions, and geochronological studies

The Aerhada Pb–Zn–Ag deposit is on the western margin of the Great Xing’an Range in NE China. Prior studies on this deposit lack information regarding precise mineralization age and convincing genetic interpretation, which limits both the prospecting at Aerhada and the reconstruction of the regional metallogenic evolution. Based on a detailed field investigation and microscopic observation, in this study, our aim was to determine the origin and evolution of the hydrothermal system and the timing of magmatism and mineralization, as well as to develop a possible metallogenic model, by revealing information regarding the mineralization paragenetic relationship, fluid inclusions, H–O–C–S–Pb isotopes, and sphalerite Rb–Sr and zircon U–Pb ages. Three successive mineralization stages were recognized: stage I quartz-arsenopyrite-pyrite, stage II quartz-sphalerite-galena, and stage III fluorite-calcite-pyrite. Four types of fluid inclusions were also identified in host minerals: CH4-rich two-phase, halite-bearing, vapor-rich two-phase, and liquid-rich two-phase. Fluid inclusion and microthermometric results showed that the homogenization temperatures were 287–341 °C for stage I, 237–291 °C for stage II, and 162–230 °C for stage III, with respective salinities of 1.7–40.2 wt%, 6.7–10.9 wt%, and 4.2–8.8 wt% NaCl equivalent. The δ18Ofluid and δDfluid values of quartz in stage I (δ18Ofluid = 8.6–10.3 ‰, δDfluid = -126.6 to −124.3 ‰) indicated that initial magmatic water interacted with organic strata, while decreasing the values of quartz in stage II (δ18Ofluid = 3.9–6.8 ‰, δDfluid = -129.1 to −127.6 ‰) and calcite in stage III (δ18Ofluid = -3.5 to −1.0 ‰, δDfluid = -115.5 to −113.4 ‰), showing a trend of dilution and cooling by meteoric water. The negative δCfluid values (δCfluid = -15.9 to −12.6 ‰) of quartz fluid inclusions from stages I and II emphasize that organic carbon was added to the hydrothermal system through water–rock interactions. The δ34S values (δ34Ssulfides = 1.2–7.5 ‰) and lead isotope data of sulfides (206Pb/204Pb = 18.153–18.684, 207Pb/204Pb = 15.370–15.750, 208Pb/204Pb = 37.653–39.301), coupled with those of the hidden biotite granite and Devonian strata, indicate that the ore-forming material was primarily derived from magma and wall rocks. The sphalerite samples produced a Rb–Sr isochron age of 154.1 ± 3.5 Ma (2σ, MSWD = 0.82, n = 8), which was like the zircon U–Pb age of biotite granite (156.3 ± 1.4 Ma, 2σ, MSWD = 0.89, n = 14). Combining the alteration pattern, fluid inclusions, and isotopic and geochronological studies, it was concluded that Aerhada is a magma-related hydrothermal Pb–Zn deposit formed under the post-collision extension setting following the Mongol–Okhotsk Ocean closure during the Late Jurassic period. The proposed metallogenic model is expected to assist in the exploration and development of polymetallic mineralization in the Great Xing’an Range.

Ore deposit prospecting using the chlorine and bromine secondary dispersion halos

The Cland Brions, that form complex compounds with metals, produce secondary dispersion halos in the hypergenesis zone at Au, Ag, Cu, Pb, and Zn ore deposits which ore bodies are controlled by fracturing and fault structures. The appearance of anomalies of the highly mobile water-soluble ions, manifested on the surface and in the wall rocks, is explained by their transfer from the deep sources to the surface by a gas flow. The migration of the ions to the earth's surface and further into the atmosphere is influenced by many factors (atmospheric pressure, temperature, humidity, rock porosity, etc.) that complicate the observation results.

A giant porphyry-skarn-epithermal Mo-W-Cu-Zn-Pb-Ag metallogenic system in the Nannihu ore field, southern North China Craton: Constraints from new geochronological and pyrite geochemical data

The southern North China Craton owns substantial Mo, W, Zn, Pb, Cu, and Ag resources, and most of them are hosted in hydrothermal deposits that may co-exist in the same ore field. However, the relationship between the different types of deposits is not well-constrained. To better understand this, here we present a comprehensive geological, geochronological, and pyrite geochemical study on the Nannihu ore field in the Luanchuan district. The Nannihu ore field is largely represented by the Nannihu Mo-W deposit, Luotuoshan Zn-Cu-W deposit, and Lengshuibeigou Pb-Zn-Ag deposit. Mo-W mineralization at Nannihu occurs in the contact zone between the Nannihu intrusion and the wall rocks, showing typical characteristics of the porphyry-type deposit. Three paragenetic stages are recognized at Nannihu, including quartz-potassium feldspar stage, quartz-sulfide stage, and quartz-carbonate stage. The Zn-Cu-W orebodies at Luotuoshan are mainly layered or lens-like, occurring within the skarn zones in the Luanchuan Group. Skarn stage, polymetallic sulfide stage, and carbonate stage are revealed at Luotuoshan. Pb-Zn-Ag mineralization at Lengshuibeigou is characterized by banded sulfide veins that are hosted in the NNE-trending fault zone. Three paragenetic stages are developed at Lengshuibeigou: quartz-pyrite stage, quartz-polymetallic sulfide stage, and quartz-carbonate stage. New geochronological data confirm that the Nannihu intrusion was formed by at least two phases of magmatism including the granite porphyry (zircon U-Pb age of 145 ± 2 Ma) and the porphyritic monzogranite (zircon U-Pb ages of 142 ± 1 Ma and 140 ± 1 Ma), which accompanied by two episodes of Mo mineralization at the Nannihu deposit identified by molybdenite Re-Os dating (144.9 ± 0.7 Ma and 142.8 ± 0.6 Ma). The Luotuoshan deposit and Lengshuibeigou deposit formed at 141 ± 1 Ma to 140 ± 1 Ma and 140 ± 3 Ma to 139 ± 3 Ma revealed by U-Pb dating of garnet and monazite, respectively, which are contemporaneous with the late episode of the Nannihu intrusion and Mo mineralization. Pyrite grains of the three deposits have Co/Ni ratios higher than 1, suggesting a unified magmatic-hydrothermal origin for them. Pyrite from Nannihu and Luotuoshan is enriched in Co, Ni, Se, Mo, Mn, and Bi, whereas pyrite from Lengshuibeigou contains high Zn, Pb, As, Cu, Ag, and Au. The regular elemental distribution of pyrite in the Nannihu ore field is consistent with that of typical porphyry-related systems worldwide.Collectively, the Early Cretaceous magmatic rocks and diverse deposits in the Nannihu ore field make up a giant magmatic-hydrothermal Mo-W-Cu-Zn-Pb-Ag metallogenic system, with the porphyry, skarn, and epithermal types of mineralization displaying a zonation from inside to outside. The multi-episode magmatism and mineralization could result in the remarkable enrichment of mineral resources. The close spatial relationship among different types of mineralization in the Nannihu ore field has a significant implication for porphyry-related mineral prospecting in the southern NCC.

Origin of the Early Cretaceous Be mineralization in the Tongbai-Dabie orogen, central China

The Niangniangding Be deposit is a Be-only deposit in the Tongbai-Dabie orogen. The Be mineralization is hosted in albitized granite in the contact zone between biotite monzogranite and metasedimentary rocks. Genthelvite, a Zn-rich helvine-group mineral, is the major carrier of Be. The Niangniangding biotite monzogranite and albitized granite were emplaced at 769–766 Ma and were derived from reworking of Paleoproterozoic crust in a Neoproterozoic continental-rift setting. Hydrothermal monazite coexisting with genthelvite yields an in situ U-Pb age of 126.7 ± 1.6 Ma, demonstrating that the Be mineralization is genetically unrelated with the Niangniangding granite that was albitized by Early Cretaceous ore-forming fluids. The albitization caused an increase of Al, Na, Mn, Fe, Zn, Be and Sr contents and a decrease of Si, K, Rb and Ba contents, reflecting in the formation of spessartite, albite, genthelvite and calcite and the consumption of quartz, K-feldspar and biotite. Petrographic and geochemical evidences hint that ore-forming fluids and metals (e.g., Be, Zn, Mn) may be sourced from non-exposed Cretaceous intrusions and metasedimentary wall rocks (the Huangmailing Formation). The Early Cretaceous intrusions are related to crustal extension due to the rollback of Paleo-Pacific plate. The close spatial relation between genthelvite, calcite, and albitization indicate that the fluid composition (the availability of Na+ and CO2– 3) may have crucially controlled the precipitation of Be. Our study indicates that the Tongbai-Dabie orogen has potential for Early Cretaceous extension-related Be deposits.

Numerical simulation of ore formation within skarn-type Pb-Zn deposits: Implications for mineral exploration and the duration of ore-forming processes

Skarn-type deposits are typical hydrothermal mineral deposits distributed throughout the world with multiple metal resources and huge economic value. However, their extremely complex forming processes hinder us from further understanding their forming mechanism and exploring their economic potential. This study builds an integrated and simplified model of skarn-type Pb-Zn deposits and applies numerical simulation approach to quantitatively describe the formation of mineralization, analyzing the continuous dynamic changes of the concentrations of generated garnet, diopside and galena/sphalerite within the system. This numerical model includes chemical reactions, heat conduction, fluid-flow, materials migration and diffusion and their complex coupled relationships. The results show that the alterations at the contact of wall rocks and intrusions have clear zoning of garnet and diopside, and the amount of diopside exceeds that of garnet at the distal end of the generated alteration zone; the generation processes of garnet, diopside and galena/sphalerite follows a strict chronological order, controlling the variation of rock porosity; the cooling process of P3 (Fig. 4b) from 700 °C to 170 °C costs 55,000 years, within which the formation of galena/sphalerite merely lasts 30,000 years, meaning that the effective lifespan of Pb/Zn mineralization takes up only 54.54 % of the whole 55,000 years. All these results provide useful information for metallogenic research of skarn-type Pb-Zn deposits as well as magmatic-hydrothermal system. However, the method applied in this research still has limitations, such as the restriction from the single-period magmatic activity, the law of mass action, and the simplified chemical equations. Future development into both mathematical geosciences and geological analytical tests will definitely provide more appropriate calculation models and testing data with higher precision, improving the accuracy and practical significance of numerical simulation of ore formation, and providing more detailed quantitative answers for remaining hot issues related to economic geology research.

Metallogenic model of the Eocene Santa María and Antares Zn-Pb(-Ag) skarn deposits, Velardeña Mining District, Durango, Mexico

The Santa María and Antares Zn-Pb(-Ag) skarn deposits in the Velardeña Mining District are located in central–NW Mexico. They lie 470 m apart along the contact between Oligocene felsic intrusions and Cretaceous limestones, and were developed during prograde, retrograde, post-ore (Santa María), and late stages. Firstly, the prograde stage was formed by fluids at ~ 600 °C and 15 wt% NaCl equiv., and consists of garnet + wollastonite ± clinopyroxene and biotite ± K-feldspar assemblages. Secondly, the retrograde/ore stage was formed by fluids at 300–500 °C with salinities of 20–30 wt% CaCl2 (Santa María) and > 40 wt% NaCl equiv. (Antares). It comprises assemblages of chlorite, amphibole, epidote, calcite, scapolite, quartz, sericite, adularia, fluorite, and muscovite associated with sphalerite, pyrite, galena, pyrrhotite, arsenopyrite, chalcopyrite, and Pb-Bi-Sb sulfosalts. Thirdly, the post-ore stage was formed by fluids at ~ 400 °C and 20–30 wt.% CaCl2 and comprises poorly mineralized calcite veins. Fourthly, the late stage was formed by fluids at < 300 °C and 20–30 wt.% CaCl2 (Santa María) and ~ 15 wt% NaCl equiv. (Antares), and crystallized tetrahedrite-group minerals and pyrite + marcasite. δ18Ofluid between ~ 14‰ and 23‰ at Santa María and between ~ 12‰ and 17‰ at Antares show a less-modified magmatic affinity for mineralizing fluids at Antares; δ13Cfluid between 0‰ and –6‰ register recycling of sedimentary C. Moreover, sulfides with δ34SVCDT between –3‰ and 2‰ reveal a magmatic source for S. Altogether, these data suggest that, at Santa María, magmatic-derived fluids actively interacted with the wall rocks, whereas at Antares the fluid-rock interaction was milder. In both deposits, metal deposition was triggered by the cooling and neutralization of ore-bearing fluids with carbonate rocks. Our 40Ar/39Ar dates for adularia of ca. 37.5 Ma place the deposits within the Eocene–early Miocene metallogenetic epoch of central–NW Mexico, during which other world-class skarn-epithermal systems were emplaced (e.g., Concepción del Oro and Mazapil-Peñasquito).

Study on slope stability under excavation and water storage based on physical model tests

Understanding the characteristics and mechanism of slope deformation caused by slope excavation and water storage is very important in the stability analysis of slope engineering. Therefore, based on similarity theory, a physical model test of excavation and water storage was established, and the deformation characteristics of the slope (three-stage excavation and five-stage water storage) were studied by using the monitoring technology of multiple measuring devices. The variation characteristics of the displacement, stress and pore water pressure in the slope were revealed. The results show that the contents of cement and yellow sand can regulate the physical, mechanical and hydrological properties and that gypsum and hydraulic oil have an effect on the permeability. Excavation leads to deformation of the rock mass in the middle and lower slope to the outside of the slope. This is attributed to the stress release, and local stress concentration occurs at the foot of the slope after redistribution. Moreover, the rock mass located in the fault zone shows nonglobal movement because the hanging wall rock mass will produce relative dislocation along the fault zone under self-gravity. Under water storage, the slope body is affected by the hydrostatic pressure, and transient compaction deformation occurs first. As water permeates into the slope body, the water weakens the rock mass, resulting in the gradual deformation of the rock mass near the slope surface to the outside of the slope. The above model test results can provide a valuable reference for slopes stability analysis in construction and subsequent operation.

Magma and fluid sources in an intracontinental porphyry system: A case study of the Relin Mo–W(–Cu) deposit, southern Yidun terrane, SW China

The Relin Mo–W (–Cu) deposit in the northern Sanjiang area is bound to a Late Cretaceous intracontinental porphyry showing variable alteration. Here we present whole-rock chemistry and Sr, Nd, Pb, Li, and B isotope data to constrain the sources of ore-magmas and to understand how magmatic-hydrothermal processes mobilize the ore elements and alter the magmatic rocks. Chemical variations indicate the ore-bearing porphyries reflect two processes: fractional crystallization and late-magmatic alteration. Fresh and weakly altered porphyries are metaluminous to weakly peraluminous, showing I-type affinity. Chemical variation among these rocks can be explained by fractional crystallization. Most of these rocks show narrow ranges of isotopic compositions with –8.6 to –6.6 for εNd80, 0.70660 to 0.71028 for 87Sr/86Sr80, and high 207Pb/204Pb80 (15.57–15.66) and 208Pb/204Pb80 (39.21–39.51) values at 206Pb/204Pb80 values of 17.37 to 18.96. The chemical and isotopic compositions of these rocks indicate that the porphyries represent mantle melts that mixed with partial melts from the Paleoproterozoic crust. Fresh and weakly altered porphyries have uniform δ7Li (–2.3 to 1.5 ‰) and δ11B (–8.0 to –12.0 ‰). The strong sericite alteration of the porphyries resulted in the loss of Na2O and Sr (breakdown of feldspar) and the strong enrichment of the ore elements Cu, Mo, W, and Sn. Porphyries with varying degrees of alteration show large ranges of δ7Li (–6.0 ‰ to 11.4 ‰) and δ11B (–8.0 to –29.2 ‰). The anomalously high δ7Li and low δ11B values of the altered rocks indicate that the intrusions drove the flow of external fluids that altered the magmatic rocks and leached the ore elements W, Mo, Cu, and Sn from the porphyries and possibly the local wall rocks.

The Mechanism of Fluid Exsolution and Sn–W Precipitation: Example from the Hongling Pb–Zn Polymetallic Deposit and the Surrounding Area in Northern China

Metal migration and precipitation in hydrothermal fluids are important topics in economic geology. The Hongling polymetallic deposit comprises one of the most important parts of the Huanggangliang–Ganzhuermiao polymetallic metallogenic belt, which is in eastern Inner Mongolia. Except for lead–zinc skarn, minor cassiterite in the skarn and disseminated W–Sn mineralization in granitic rocks have also been found. The dominant Sn–W mineralization is in the northern part of the deposit, occurring as disseminated wolframite and cassiterite in aplite hosted in Mesozoic granite porphyry. The aplite together with pegmatite K-feldspar–quartz comprises vein dikes hosted in the granite porphyry, providing evidence for the transition from melt to fluid. The veins, dikes, and Sn–W mineralization in the aplite provide an opportunity to investigate fluid exsolution and the mechanics of metal precipitation. Based on field observations, the micrographic and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) results of the vein dikes, chronology, and the whole-rock geochemistry of the host rock, together with the fluid inclusion results, this paper discusses the characteristics of the causative magma, the mechanics of fluid exsolution and W–Sn precipitation. Our results show that the causative magma is of highly fractionated A-type granite affinity and has an intrusive age of late Mesozoic (133.3 ± 0.86 Ma). The magmatic evolution during shallow emplacement led to immiscibility between highly volatile, high-silica, and W- and Sn-enriched melts from the parent magma, followed by fluid exsolution from the water-rich melt. The alkaline-rich fluid exsolution led to a change in the redox state of the magma and the chilling of the melt. Fluid boiling occurred soon after the fluid exsolution and was accompanied by the degassing of CO2. The boiling and escape of CO2 from the fluid led to changes in fluid redox and W and Sn precipitation; thus, the W and Sn mineralization are mostly hosted in causative intrusions or peripheral wall rocks, which can be used as indicators for Sn–W exploration in the area.

Genesis of the Yi’nan Tongjing Gold–Copper Skarn Deposit, Luxi District, North China Craton: Evidence from Fluid Inclusions and H–O Isotopes

The Luxi district presents an exceptional research area for the investigation of the significant role played by magma exsolution fluids in the mineralization process of Au–Cu deposits. A particularly noteworthy occurrence within this region is the Yi’nan Tongjing Au–Cu skarn deposit, situated in the central-southern part of the Luxi district. This deposit primarily occurs in the contact zone between the early Cretaceous Tongjing complex and the Proterozoic to Cambrian sequences. The ore formation process observed in this deposit can be categorized into three distinct stages: (I) thermal metamorphism, (II) prograde alteration, and (III) retrograde alteration. The retrograde alteration stage is further divided into four sub-stages: late skarn (III-1), oxide (III-2), sulfide (III-3), and late quartz-calcite (III-4). It is primarily during the III-3 sub-stage that gold mineralization occurs. Petrographic analysis has identified three types of fluid inclusions (FIs) within garnet, quartz, and calcite grains. These include liquid-rich two-phase aqueous FIs, vapor-rich two-phase aqueous FIs, and halite-bearing multi-phase FIs. The homogenization temperatures of fluid inclusions from stages II, III-3, and III-4 range between 430–457 °C, 341–406 °C, and 166–215 °C (first to third quartiles), respectively. The garnet samples from stage II exhibit hydrogen and oxygen isotope compositions (δ18OH2O = 6.8‰ and δD = −73‰) that are indicative of a typical magma source. However, the hydrogen and oxygen isotopes of sub-stages III-1, III-2, and III-3 (δ18OH2O = 7.32‰ to 9.74‰; δD = −107‰ to −81.9‰) fall below the magma water box while the hydrogen and oxygen isotope values of III-4 (δ18OH2O = −5.3‰ to −0.9‰ and δD = −103.8‰ to −67‰) tend to move towards the meteoric water line. Furthermore, the ore-forming fluid displays characteristics of a mixture between the crustal and mantle fluids. The Tongjing complex occurred along a weakened fault zone, initiating a process of thermal metamorphism upon contact with the wall rock. This thermal metamorphism resulted in the formation of diverse assemblages, including hornfels, reaction skarns, and skarnoids. Subsequently, the upward movement of ore-forming fluids triggered exsolution which led to the establishment of a high-temperature, medium-salinity NaCl–H2O system with a single phase at depths ranging from 1–3 km. This marked the formation of the prograde alteration stage. Afterward, the ore-forming fluid underwent water–rock interactions and the admixture of meteoric water at a depth of 1–2 km. These processes facilitated phase separation, commonly referred to as boiling, resulting in the transformation of the ore-forming fluid into higher salinity fluids and lower-density gases. This evolutionary transition ultimately induced the precipitation and liberation of gold and copper from the fluid.