Porphyry Copper Research Articles

Geochronology and petrogeochemistry of Miocene porphyries from the Beimulang deposit, western Gangdese copper belt

The Beimulang deposit, a newly discovered large porphyry copper deposit, containing 1.3 Mt @ 0.38% Cu, prominently features mineralized orebodies and hydrothermal alteration in the monzogranite porphyry. Zircon U-Pb dating reveals ages of 14.4–14.0 Ma for the monzogranite porphyry and 11.2–11.0 Ma for the granite porphyry. A consistent Re-Os age of 14.1 ± 0.4 Ma from molybdenite suggests a possible link between mineralization and the monzogranite porphyry. The Beimulang Miocene porphyries are rich in SiO2 (70.01–72.81 wt%) and Sr (217–864 ppm) and have high Sr/Y ratios (26–139), which were originated from partial melting of the subduction-modified Tibetan juvenile lower crust. The Beimulang Miocene porphyries show high log w(Fe2O3/FeO) values (>0) in whole rock and high δEu values (mostly > 0.3), high ΔFMQ (4.32–6.43) in zircons, suggesting a high oxidation state. The Beimulang Miocene porphyries show high V/Sc ratios in whole rock and high 10,000 × (δEu)/Y, high (Ce/Nd)/Y, low Dy/Yb ratios (i.e., mostly > 13, > 4, > 0.02 and < 0.3, respectively) in zircons, indicating they are notably hydrated. The granite porphyry has lower εNd (t) (0.70849 – 0.70996) values and higher (87Sr/86Sr)i (-9.3 – -7.8) in whole rock, lower εHf (t) (-5.25 – -2.70) and higher U/Yb (6.0–18.3), δ18O (6.42–7.57‰) in zircon than the monzogranite porphyry (εNd(t) = -5.52 – -4.45; (87Sr/86Sr)i = 0.70744–0.70818; εHf (t) = -3.24 – -0.92; U/Yb = 2.62–8.96; δ18O = 6.10–7.53‰), indicating that the granite porphyry contains fewer juvenile materials compared to the monzogranite porphyry. The high-Mg dioritic rocks in the Beimulang-Zhunuo area reveal significant correlations with monzogranite porphyry rather than granite porphyry in terms of Sr, Sr/Y, Dy/Yb, δEu and SiO2 contents. Taking into account the contemporaneous presence of high-Mg dioritic rocks with the monzogranite porphyry, which are not contemporaneous with the granite porphyry at Beimulang, it can be inferred that these diorite magmas played a significant role in forming the Miocene monzogranite porphyry rather than granite porphyry. Accordingly, the low fertility of the granite porphyry is possibly due to the limited contribution of juvenile melts and lack of the dioritic magmas.

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

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

Early zircon saturation in adakitic magmatic differentiation series and low Zr content of porphyry copper magmas

Porphyry copper ore-forming magmas worldwide are chemically distinguished from ordinary arc granitoids by lower Zr and by higher Sr/Zr ratios at equivalent SiO2 contents. Low ppm Zr in zircon-saturated melts and high whole-rock Sr/Zr in granitoid samples retaining igneous plagioclase are useful discriminants of Cu-fertile intrusive complexes. These and other chemical discriminants of porphyry-copper-forming melts of tonalite-granodiorite-adamellite composition cannot develop during crystallisation-differentiation at upper-crustal pressures. They indicate unusually high dissolved H2O (≥ 9 wt%) in residual melts at depths near the base of the crust. We compare Zr behaviour during mafic-to-felsic magmatic differentiation in orogenically deforming, copper-mineralised arc segments with behaviour during differentiation in non-orogenic, unmineralised arc segments laterally adjacent along the same subduction zones. In orogenically deforming segments, horizontal compressive stress provides resistance to opening of tensile dyke fractures and promotes entrapment of mantle-derived basaltic melts in magma chambers embedded in hot country rock at Moho-vicinity depths, where magmas cool slowly and residual melts tend to last long enough to experience intermittent chamber replenishment by basaltic melts from the deeper mantle. Over several cycles of replenishment and fractional crystallisation, residual melts acquire high concentrations of inherited chemical components that were largely excluded from cumulus minerals—H2O, Cl, CO2, SO3, etc. Accumulating H2O re-orders the high-pressure crystallisation sequence of igneous minerals in successive cycles and leads to early and prolific production of hornblende and early zircon saturation in mafic melts (< 60 wt% SiO2) of later cycles and leads to low Zr contents of zircon-saturated intermediate-composition residual melts.

The Genetic Features and Flotation Properties of Porphyry–Copper–Gold Ore (Malmyzh Deposit, Khabarovsk Krai, Russia)

The Genetic Features and Flotation Properties of Porphyry–Copper–Gold Ore (Malmyzh Deposit, Khabarovsk Krai, Russia)

Spatial Overlay Analysis of Geochemical Singularity Index α-Value of Porphyry Cu Deposit in Gangdese Metallogenic Belt, Tibet, Western China

The statistical modeling with ILR-RPCA-back CLR has two problems when dealing with the closure effect of geochemical data. Firstly, after performing isometric logratio (ilr) transformation, robust principal component analysis (RPCA) is employed for processing. The double-plot diagram illustrates that the element sequence transformation occurs in the first and second principal components, while the unique principal component remains unattainable. Secondly, by transforming both the score and load into the centered logratio (CLR) space using the U matrix, it is possible to obtain a score result that corresponds to the original order of elements according to the CLR = ILR·U formula. However, for obtaining a load result that corresponds to the original order of elements, an alternative formula “CLR = UT·ILR” must be used instead. In order to determine the optimal element assemblage for porphyry copper deposits, this study conducted statistical analysis on mineral assemblages from discovered deposits in the Gangdese metallogenic belt and identified Cu, Mo, Au, Ag, W, and Bi as key elements associated with porphyry copper deposits. Subsequently, by analyzing the singularities of the composite elements, the spatial overlay of the combined element is carried out, and concentration-area (C-A) fractal filtering is applied to identify the anomaly and background areas. To facilitate comparison, we conducted an analysis of various mineral and ore deposit types, revealing the following findings: (1) Combination elements exhibit superior recognition capability than single elements in porphyry copper deposits; (2) Skarn-type copper deposits unrelated to porphyry show a high degree of dissimilarity compared to those related to porphyry; (3) this method offers advantages over the single element method in evaluating porphyry gold deposits by reducing anomaly levels and initial investment during the evaluation stage for porphyry copper anomalies; (4) However, this method has limited ability in distinguishing between porphyry copper and molybdenum deposits.

The propylitic alteration in the Ponce Enriquez Gold Mining district, Azuay province, Ecuador: genetic constraints from a mineral chemistry and fluid inclusions study

Wide areas of the Southern sector of Ecuador are characterized by Cretaceous mafic volcanic rocks, pervasively altered by a propylitic mineralogical assemblage with epidote, chlorite, and quartz with minor titanite, illite and prehnite. These propylitically altered rocks host significant gold mineralization in veins, deeply exploited in the last decades. Porphyry Au-Cu deposits also occur in the area. This work focuses on the study of this propylitic alteration to assess the genetic conditions and the relation with the distance from the porphyry system, through the chemical composition of the secondary minerals (particularly trace elements in epidote and chlorite) and fluid inclusion data. The aim is to improve knowledge of the trace element geochemistry of secondary minerals in propylitic alteration and their relationship to the causative porphyry systems. The results of this work indicate that alteration affecting the rocks of the Pallatanga Fm. can be related to the propylitic hydrothermal alteration halo of porphyry copper deposits. Fluid inclusion investigation in quartz veins associated with epidote and chlorite evidenced at least two pulses of hydrothermal fluids characterized by temperature around 345°C for the first one and around 305°C for the second one. The salinity of the fluids is always low (around 1.5 wt% NaClequiv.) suggesting a dominantly meteoric component. Evidence of boiling processes have not been observed. We hypothesize that the hydrothermally altered “green rocks” of the Ponce Enriquez Mining District could be envisaged as the propylitic halo of the Miocene hornblende-bearing Au-Cu porphyry deposits of Gaby-Papa Grande, and discuss the epidote and chlorite trace element composition in this scenario. The results help improving the general knowledge of the propylitically altered rocks in southern Ecuador and add new data for the use of trace element chemistry of epidote and chlorite in mineral exploration elsewhere.

GIS-based mineral prospectivity mapping using machine learning methods: A case study from Zhuonuo ore district, Tibet

The Zhunuo ore concentration area (ZOCA) is the most potential prospective area of Cu-Au (Mo) in the west of the southern subterrane, Tibet. Single traditional prospective methods (e.g., stream sedimentary geochemistry) often produced larger area and false abnormal information in the Gangdese orogenic belt because of the high altitude and the intense weather and erosion, which can not meet the urgent demand of the current situation for Cu resources. In this study, we combinedamineral system approachwith GIS-basedmachine learningapproachsto obtain geologically meaningful mineral prospective maps. The detail steps include: (i) establishing the mineral system conception model of porphyry copper deposits (PCDs); (ii) transforming the targeted porphyry metallogenic system components into spatial proxies associated with the crucial ore-forming processes; (iii) extracting the spatial proxies: proximity to intrusive rocks (source), NE orientation faults (transport and/or physical trap), Fe-oxide and propylitization hydrothermal alterations zone (hydrothermal fluids) and the metallogenic strength diagram of Cu-Mo-W-Bi-Au-Ag-Pb-Zn (deposition); (iv) Radial Basis Functions Link Networks (RBFLN), Random forests (RF) Supervised and Fuzzy Clustering (FC) unsupervised machine learning methods were applied to capture the complex and crucial mineralization information between known deposit types and evidence layers; (vi) model estimation and delineating prospective potential targets: Receiver operating characteristic curve (ROC), predictive-area (P-A) plotting and normalised density (Nd) were used to evaluate the predictive models results. The results indicate that the RBFLN model, RF model, and FC model show high predictive accuracy. The AUC values under the ROC area of the RBFLN model, RF model, and FC model are 0.99, 0.96, and 0.94, respectively. The RBFLN model outperforms the RF model and FC model, the predictive-area plotting of RBFLN occupies 12% of the study area containing 88% of the known deposits. The predictive-area plotting of the RF model and FC model showed that 14% and 21% of the study area contained 86% and 79% of the known deposits, respectively. The normalized density (Nd) of a layer is defined as the ratio of the prediction success rate (Pr) of the P-A plotting to the corresponding area (Oa). The normalized density of the RBFLN model, the RF model, and the FC model are 7.33, 6.14, and 3.76, respectively, which revealed that the results of the three predictive models all have positive indications. These studies show that RBFLN supervised machine learning method is a more robustness and generalization capability. The predictive results also provide prospective potential targets (e.g., northern Cimabanshuo, northwest Wubaduolai, and southwestern and western Zhunuo PCD) for further exploration, and this method can be also applicable to other mineral systems and districts.

The formation of a giant post-collision porphyry copper system: A case study of the Jiama deposit, Tibet

The large magma reservoirs underlying world-class porphyry deposits are one of the key factors in their formation, which thus led to the present study focusing on the unmineralized intrusive rocks underlying the porphyry molybdenum-copper orebody of the post-collisional Jiama porphyry-skarn copper-polymetallic deposit in southern Tibet. The Jiama porphyry intrusion comprises intermediate-silica quartz diorite, monzogranite, and granodiorite porphyries, as well a high-silica granite porphyry. The intrusive rocks suite exhibits similar whole-rock Sr-Nd isotopic compositions [εNd(t) = −3.9 to −0.8], suggesting a common, non-radiogenic magma source. Yet, these rocks have distinct geochemical characteristics. The intermediate-silica rocks are relatively enriched in Ba and Sr with minor Eu anomalies, and show adakite-like geochemical characteristics. In contrast, the high-silica granite porphyry is strongly depleted in Ba, Sr, and Eu, and lacks adakite-like geochemical characteristics. We propose that the high-silica granite porphyry represents highly fractionated melt extracted from a silicic mush reservoir (crystallinity of ∼40%−65%), and that the monzogranite and granodiorite porphyries constitute the complementary residual silicic cumulates. High crystallinity facilitates the formation of connected fluid pathways, allowing the efficient removal of volatiles from the remaining silicic melt and a rapid flux of the ore-forming fluids toward the apical parts of the large magma reservoir. Less-evolved mafic melt is believed to have repeatedly intruded the base of the magma reservoir, thereby releasing volatiles and water into the silicic mush systems. The volatiles migrated upward through the fluid channels and accumulated in the apical part of the magma reservoir, subsequently, as a result of the overpressure in the roof zone, ore-forming fluids and successive batches of magma were expelled together, thereby forming the Jiama porphyry-skarn deposit.

Clay minerals characterization of the Miduk ball mill output through spectral analysis

Porphyry copper deposits usually include typical alteration types, which are often composed of clay minerals. The mixing of clay minerals has a significant impact on their spectral absorption characteristics, and their identification and separation becomes complicated. One of the most accurate and widely used methods for identifying minerals is spectroscopy, which is a suitable alternative to traditional methods. Spectroscopy assists in identifying the mineral composition and classification. The aim of the following research is to quantitatively characterize clay minerals in mineral assemblage of ball mill output. Pure and composite samples were prepared through sampling from two alteration types and creating synthetic samples containing different percentages of clay minerals. Then they were subjected to spectral analysis in the range of 2500–350 nm and their output was subjected to necessary pre-processing. The results were used for classification by employing a hybrid algorithm. The analysis identified the following minerals in the Miduk deposit: hematite, carbonates, illite, biotite, kaolinite, chlorite and muscovite. Additionally, microscopic studies were conducted on the samples for further analysis. Finally, total and clay diffraction XRD analysis were used to validate the results.

Mapping hydrothermal alteration of the Pulang porphyry copper deposit, SW China, using ASTER and ZY1-02D satellite data

Alteration minerals are important prospecting indicators, and multispectral and hyperspectral remote sensing technologies are important prospecting tools. Multispectral remote sensing data such as ASTER have been widely used for extracting alteration mineral information. The dataset is easy to access, cost-effective to use, and rich in rock and ore spectrum information. Recently, the use of alteration mineral identification technology and hyperspectral satellite data for fine prospecting has become feasible in China, considering the development of hyperspectral remote sensing technology, especially the launch of the ZY1-02D satellite in China. Pulang porphyry copper deposit, Southwest China, is a largescale, explored deposit with unclear peripheral prospecting. Therefore, principal component analysis (PCA) and mixed tuned matched filtering (MTMF) methods were used in this study to extract the mineralized alteration minerals of the Pulang porphyry copper deposit area from the ASTER multispectral data and ZY1-02D hyperspectral data. Then, Al-OH and Fe-Mg-OH alteration information was obtained from the ASTER data using the PCA method. Meanwhile, sericite, chlorite, and epidote alteration information was extracted using the MTMF method and ASTER data. With the ZY1-02D data, the alterations of sericite, chlorite, and epidote were extracted by the PCA and MTMF methods. A field verification showed that the overall accuracy of the ASTER-based alteration extraction was up to 0.57, and the overall accuracy of the ZY1-02D-based alteration extraction was up to 0.88. And circled six favorable areas of copper deposit based on alteration mapping. Therefore, the ZY1-02D data can be regarded as a reliable and promising tool for delineating potential prospecting areas according to the mapping of hydrothermal alteration information, which can be explored further in the prospecting field in the future. The eastern and northern parts of the first mining area should be further explored for potential prospecting.

Development of a Hybrid Fixed-Wing UAV Aeromagnetic Survey System and an Application Study in Chating Deposit

In recent years, the development of airborne magnetic survey technology based on unmanned aerial vehicles (UAVs) has been rapidly advancing. The commonly used systems are the fixed-wing UAV-based, multi-rotors UAV-based, and unmanned helicopters-based magnetic survey systems. And, a type of hybrid UAV that uses a vertical takeoff and landing (VTOL) and fixed-wing cruise mode is increasingly being used to carry airborne magnetic survey systems. To meet the requirements of most UAVs for small-sized and lightweight payloads, a miniature magnetic survey system was developed and integrated into a hybrid fixed-wing UAV and formed an aeromagnetic survey system. And, a peripheral mineral exploration test was conducted in a known porphyry copper–gold deposit in southeastern China using the system. By processing the collected magnetic data with 3D inversion of susceptibilities, potential ore-bearing intrusive rocks were quickly identified and delineated, providing clues for peripheral mineral exploration in the mining area.

Lithium-Rich Pegmatite Detection Integrating High-Resolution and Hyperspectral Satellite Data in Zhawulong Area, Western Sichuan, China

Lithium (Li) has grown to be a strategic key metal due to the enormous demand for the development of new energy industries over the world. As one of the most significant sources of Li resources, pegmatite-type Li deposits hold a large share of the mining market. In recent years, several large and super-large spodumene (Spd)-rich pegmatite deposits have been discovered successively in the Hoh-Xil–Songpan-Garzê (HXSG) orogenic belt of the northern Tibetan Plateau, indicative of the great Li prospecting potential of this belt. Hyperspectral remote sensing (HRS), as a rapidly developing exploration technology, is especially sensitive to the identification of alteration minerals, and has made important breakthroughs in porphyry copper deposit exploration. However, due to the small width of the pegmatite dykes and the lack of typical alteration zones, the ability of HRS in the exploration of Li-rich pegmatite deposits remains to be explored. In this study, Li-rich pegmatite anomalies were directly extracted from ZY1-02D hyperspectral imagery in the Zhawulong (ZWL) area of western Sichuan, China, using target detection techniques including Adaptive Cosine Estimator (ACE), Constrained Energy Minimization (CEM), Spectral Angle Mapper (SAM), and SAM with BandMax (SAMBM). Further, the Li-rich anomalies were superimposed with the distribution of pegmatite dykes delineated based on GF-2 high-resolution imagery. Our final results accurately identified the known range of Spd pegmatite dykes and further predicted two new exploration target areas. The approaches used in this study could be easily extended to other potential mineralization areas to discover new rare metal pegmatite deposits on the Tibetan Plateau.

A Model for the Lithospheric Architecture of the Central Andes and the Localization of Giant Porphyry Copper Deposit Clusters

Abstract In the central Andes, giant porphyry copper deposits of similar ages group into discrete geographic clusters that are regularly spaced and aligned within orogen-parallel belts. This clustering highlights how exceptional geologic processes affected localized regions of the lithosphere during mineralization and that the spatial and temporal distribution of giant porphyry deposits is nonrandom. Development of favorable regions of lithosphere for significant metal concentration are linked to the overlap of structural pathways that focus fluid and magma flow from the mantle to upper crust during high-horizontal-compressive-strain events. These structural pathways are notoriously difficult to identify in the field due to their often-subtle surficial manifestations and continental scale. Field mapping at multiple scales in northwest Argentina and southern Peru, as well as regional structural traverses throughout the central Andes, indicates the presence of regional-scale structural corridors 5 to 25 km wide and hundreds of km long that consist of myriad fault planes. The variable width and diffuse surface expression of these corridors is interpreted to reflect the upward propagation of underlying zones of basement weakness through younger supracrustal sequences in the overriding plate. Such structural corridors are (1) apparent at multiple scales of investigation, (2) long-lived, (3) preferentially reactivated though time, and (4) evident in geophysical data sets. This structural architecture formed in response to the interplay of pre-Cenozoic tectonics and the orientation of inherited structural weaknesses. These fault systems persist in the upper crust as steep zones of enhanced permeability that can preferentially reactivate as pathways for ascending hydrous magmas and fluids during major deformation events. Linear orogen-parallel structural belts cogenetic with the magmatic arc provide the first-order control to giant porphyry copper deposit distribution. The second-order control is the intersection of orogen-oblique structural corridors with the orogen-parallel belts, localizing deposit clusters at these intersections. Such regions are inferred to have been zones of deep permeability, with vertical translithospheric pathways activated during high-strain tectonic events that affected the intra-arc stress field.

Advances in metallogeny and tectonics of the Eastern Tethyan Realm: Introduction

The Tethys domain preserves one of the largest continent‐continent collisional orogenic belts on Earth. This belt can be divided into the Proterozoic to Palaeozoic Proto‐Tethyan orogenic belt, Late Palaeozoic to Triassic Palaeo‐Tethyan orogenic belt and Triassic to Cenozoic Meso‐ and Neo‐Tethyan orogenic belts. The Tethyan metallogenic domain, representing one of the three major metallogenic domains in the world, extends more than 10,000 km from east to west and has developed world‐class ore belts, such as the South‐east Asia tin ore belt, Sanjiang metallogenic belt in South‐west China, Gangdese–Pakistan–Iran porphyry copper belt and South‐east Europe epithermal gold belt. The geology of the Tethys domain has been studied for more than 100 years and many important advances have been made recently, although scientific issues remain controversial. This thematic section of Geological Journal contains 10 articles focusing on the formation of rocks and ore deposits, including petrology and geochemistry of magmatic, metamorphic and sedimentary rocks, and the formation mechanism of mineral deposits in the Eastern Tethyan Realm. These articles reflect new progress in related studies and provide important reference for future studies.

Genesis of the Kuh-Panj porphyry copper deposit, Kerman, Iran: Constraints from mineralization, geochemistry, fluid inclusion, and zircon U[sbnd]Pb isotope systematics

The Miocene Kuh-Panj porphyry copper deposit, with reserve estimated at about 100 Mt. at 0.21 % Cu, is located 120 km SW of Kerman in the southern part of the Urumieh-Dokhtar magmatic arc. The Eocene host rocks consist of tuff, lithic tuff, breccia tuff, and lava flows, ranging in composition from rhyodacite to andesite. A late Miocene granodiorite porphyry stock (8.57 ± 0.49 Ma, U/Pb zircon) intruded into the Eocene sequence. Subvolcanic dykes cut the Eocene rocks and porphyry stock. The Kuh-Panj porphyry system has an extensive and typical hydrothermal alteration zoning pattern, which is comprised of potassic, phyllic, argillic, and propylitic alteration types from inner proximal to outer distal zones. Copper mineralization occurs in potassic and to some extent in phyllic zones. Mineralization is mostly observed as disseminated, stockwork, and vein-veinlets forms in the porphyry stock. Vein paragenesis includes barren quartz, M-type (magnetite+biotite), A1-type (quartz+magnetite+chalcopyrite±chlorite±biotite), A2-type (quartz+chalcopyrite±pyrite), D-type (quartz+pyrite±chalcopyrite), and L-type (galena+sphalerite±chalcopyrite±pyrite) veins. The I-type granitoids with calc-alkaline affinity have enrichments of LILE (Pb, K, U, Sr, and Cs), depletion of HFSE (P, Nb, Ta, Zr, and Ti), and enrichment in LREE displaying geochemical similarity to arc-related magmatic rocks. The high SiO2 (ave. 68.9 wt%), high Al2O3 (ave. 14.5 wt%), low MgO (ave. 1.3 wt%), low P2O5 (< 0.2 wt%), high Sr (ave. 365 ppm), high Sr/Y (ave. 45), relatively high LaN/YbN (ave. 28), relatively high Th (ave. 8 ppm), low Y (ave. 8 ppm), and low Yb (0.5 ppm) contents are similar to those of fertile porphyries and lower crust-derived adakites. The most dominant type of fluid inclusions in quartz from mineralized veins are liquid-vapor-halite-solid (LVHS), liquid-vapor-halite (LVH), liquid-vapor (LV), and vapor-liquid (VL) fluids. Homogenization temperatures of LVHS, LVH, LV, and VL fluids range from 306 to 574 °C, 141–566 °C, 215–422°, and 349–571 °C, respectively. Salinities of LVHS, LVH, LV, and VL fluid inclusions range from 30 to 69, 29.0–65.5, 0.35–22.0, and 0.7–13.0 wt% NaCl eq., respectively. The extreme variations in salinities of fluid inclusions represent the combined effects of varying salinity of the magmatic fluid, aqueous fluid-phase immiscibility (boiling), and mixing with lower salinity meteoric water later in the cooling history of the porphyry system. Normal cooling, water-rock interaction, surface fluid dilution, and boiling are dominant factors that control both the distribution and abundance of mineralization. Zircon from the Kuh-Panj system has high Th/U (0.53 to 0.83), low Dy/Yb (<0.3) ratios, positive Eu/Eu* (1.28–1.85), strong positive Ce/Ce* (1.36 to 197) reflecting high Ce4+/Ce3+ ratios, and enrichment in HREEs relative to LREEs, which indicate the magmatic origin of zircon, oxidized, and hydrous conditions of the primary magma. This magma with adakitic affinities is favorable for producing fertile porphyry systems. Based on these multidisciplinary studies, the Kuh-Panj deposit is classified as a continental arc-related porphyry copper system hosted predominantly at the transition zone between potassic and phyllic alteration zones due to decreasing temperature, boiling, and fluid-rock reaction that all enhance CuFe sulfide saturation.

Improving the performance of a low-grade porphyry copper ore flotation plant using a simulator that can predict grade vs. recovery curves

A large porphyry copper flotation plant has been simulated using a flotation model developed from first principles using the hydrophobic force as a kinetic parameter (Huang et al., 2022; Gupta et al., 2022). The input to the simulation was the size-by-class liberation matrix (mij) of a flotation feed, which was essential for predicting the size-by-class flotation rate constants (kij) and hence grade vs. recovery curves for the flotation bank. The model can be used to predict the performance of a flotation circuit provided that mij matrices are available for the feeds to the flotation banks in the circuit. With limited information on feed characteristics, we carried out a circuit simulation of the plant with some simplifying assumptions. The results suggest that significant financial benefits can be gained by recovering the slow-floating particles from the cleaner-scavenger tails that constitute the circulating load using an advanced separation technology in a separate copper recovery unit. With this approach, it is possible to substantially increase the throughput while maintaining copper recoveries and concentrate grades.

Machine Learning (ML)-Based Copper Mineralization Prospectivity Mapping (MPM) Using Mining Geochemistry Method and Remote Sensing Satellite Data

The exploration of buried mineral deposits is required to generate innovative approaches and the integration of multi-source geoscientific datasets. Mining geochemistry methods have been generated based on the theory of multi-formational geochemical dispersion haloes. Satellite remote sensing data is a form of surficial geoscience datasets and can be considered as big data in terms of veracity and volume. The different alteration zones extracted using remote sensing methods have not been yet categorized based on the mineralogical and geochemical types (MGT) of anomalies and cannot discriminate blind mineralization (BM) from zone dispersed mineralization (ZDM). In this research, an innovative approach was developed to optimize remote sensing-based evidential variables using some constructed mining geochemistry models for a machine learning (ML)-based copper prospectivity mapping. Accordingly, several main steps were implemented and analyzed. Initially, the MGT model was executed by studying the distribution of indicator elements of lithogeochemical data extracted from 50 copper deposits from Commonwealth of Independent States (CIS) countries to identify the MGT of geochemical anomalies associated with copper mineralization. Then, the geochemical zonality model was constructed using the database of the porphyry copper deposits of Iran and Kazakhstan to evaluate the geochemical anomalies related to porphyry copper mineralization (e.g., the Saghari deposit located around the Chah-Musa deposit, Toroud-Chah Shirin belt, central north Iran). Subsequently, the results of mining geochemistry models were used to produce the geochemical evidential variable by vertical geochemical zonality (Vz) (Pb × Zn/Cu × Mo) and to optimize the remote sensing-based evidential variables. Finally, a random forest algorithm was applied to integrate the evidential variables for generating a provincial-scale prospectivity mapping of porphyry copper deposits in the Toroud-Chah Shirin belt. The results of this investigation substantiated that the machine learning (ML)-based integration of multi-source geoscientific datasets, such as mining geochemistry techniques and satellite remote sensing data, is an innovative and applicable approach for copper mineralization prospectivity mapping in metallogenic provinces.

Apatite evidence for a fluid-saturated, crystal-rich magma reservoir forming the Quellaveco porphyry copper deposit (Southern Peru)

Large volume, intermediate-felsic magma reservoirs are the source of melt and mineralising fluids which generate porphyry copper deposits. Cooling and crystallisation of hydrous magmas drives the exsolution and expulsion of a magmatic volatile phase—a process which remains challenging to constrain in porphyry Cu systems where the record of magma volatile compositions is rarely preserved. Here, we use the halogen compositions of apatite inclusions shielded as inclusions within zircon to constrain volatile evolution in magma reservoirs which pre-date and are synchronous with porphyry Cu mineralisation at Quellaveco, Southern Peru. Geochemical and textural data confirm that the zircon-included apatites escaped re-equilibration with hydrothermal fluids, unlike apatites found in the groundmass of the same rocks. We, therefore, recommend that future studies attempting to reconcile magmatic volatile budgets using apatite in porphyry Cu systems should focus on apatite inclusions in zircon. By combining the apatite inclusion data with numerical modelling, we find evidence that the magma reservoir sourcing porphyry Cu mineralisation remained fluid-saturated for the entire period recorded by apatite crystallisation. By contrast, the pre-mineralisation batholith shows more variable, potentially fluid-undersaturated behaviour. Our modelling suggests that in order to attain the porphyry melt volatile compositions inferred from apatite, the magma reservoir must have exsolved a large proportion of its volatile budget, consistent with having been held at high crystallinity (40–60% crystals). This crystallisation interval coincides with peak chlorine and copper extraction from intermediate-felsic magmas, and would have permitted efficient fluid migration and accumulation at the roof of the system. We suggest that the storage of large-volume, long-lived, crystal-rich magma reservoirs in magmatic arcs may be a critical step in generating world-class porphyry copper deposits.

Magnetotelluric investigations at Andean volcanoes: Partial melt or saline magmatic fluids?

Knowledge of the architecture of active magmatic systems is important for both volcanic hazard assessment and evaluating potential geothermal energy production and metals recovery from magmatic fluids. Increasingly, magmatic systems are imaged using the magnetotelluric method to detect electrically conductive partial melt and/or saline magmatic fluid reservoirs. We review recent magnetotelluric studies at eight Andean volcanoes, revealing electrical conductivity anomalies with variable magnitudes and locations. Six of the studied volcanoes exhibit three main electrical conductivity anomalies, located at shallow (<3 km), intermediate (≈5 km), and deep (>10 km) depths. The shallow anomalies are often thin and laterally extensive, consistent with clay cap alteration layers, while the deep anomalies are generally interpreted as partial melt reservoirs. The intermediate depth anomalies, although also often attributed to partial melt, have less clear origins. By analysing laboratory-derived electrical conductivity relationships, we show that the intermediate depth anomalies are generally most consistent with saline magmatic fluids stored in porous rock. However, other geophysical and petrological data suggest that localised partial melt also exists at intermediate depths. Therefore, the intermediate depth anomalies likely represent mixed melt and saline magmatic fluid systems, such as those responsible for forming magmatic-hydrothermal alteration zones and copper porphyry deposits. At individual volcanoes, refining the generalised three layer model proposed here by using additional geophysical or petrological data is key to constraining the resources and/or hazard potential of the magmatic system.

Biotite Geochemistry and Its Implication for the Difference in Mineralization in the Xiongcun Porphyry Cu–Au Ore District, Tibet

The Xiongcun Cu–Au ore district is in the southern middle Gangdese Metallogenic Belt, Tibet, and formed during Neo-Tethyan oceanic subduction. The Xiongcun ore district mainly comprises two deposits, the No. I and No. II deposits, which were formed by two individual mineralization events according to deposit geology and Re–Os isotopic dating of molybdenite. The No. I deposit is similar to a reduced porphyry copper–gold deposit, given the widespread occurrence of primary and/or hydrothermal pyrrhotite and common CH4-rich and rare N2-rich fluid inclusions. The No. II deposit, similar to classic oxidized porphyry copper–gold deposits, contains highly oxidized minerals, including magnetite, anhydrite, and hematite. The halogen chemistry of the ore-forming fluid from the No. I and No. II deposits is still unclear. Biotite geochemistry with halogen contents was used to investigate the differences in ore-forming fluid between the No. I and No. II deposits. Hydrothermal biotite from the No. I deposit, usually intergrown with sphalerite, is Mg-rich and classified as phlogopite and Mg-biotite, and hydrothermal biotite from the No. II deposit is classified as Mg-biotite. Hydrothermal biotite from the No. I deposit has significantly higher SiO2, MnO, MgO, F, Li, Sc, Zn, Rb, Tl, and Pb contents and lower Al2O3, FeOtot, Cl, Ba, Cr, V, Co, Ni, Y, Sr, Zr, Th, and Cu contents than the biotite from the No. II deposit. Hydrothermal biotites from the No. I and No. II deposits yield temperatures ranging from 230 °C to 593 °C and 212 °C to 306 °C, respectively. The calculated oxygen fugacity and fugacity ratios indicate that the hydrothermal fluid of the No. I deposit has a higher F content, oxygen fugacity, and log(fHF/fHCl) value and a lower log(fH2O/fHF) value than the hydrothermal fluid from the No. II deposit. The biotite geochemistry shows that the No. I and No. II deposits formed from different hydrothermal fluids. The hydrothermal fluid of the No. I deposit was mixed with meteoric waters containing organic matter, resulting in a decrease in oxygen fugacity and more efficient precipitation of gold. The No. I and No. II deposits were formed by a Cl-rich hydrothermal system conducive to transporting Cu and Au. The decreasing Cl, oxygen fugacity, and temperature may be the key factors in Cu and Au precipitation. Biotite geochemistry allows a more detailed evaluation of the halogen chemistry of hydrothermal fluids and their evolution within porphyry Cu systems.