A hybrid AHP-VIKOR approach for prospectivity modeling of porphyry Cu deposits in the Varzaghan District,NW Iran

Identifying highly favorable areas related to a particular mineralization type is the main objective of mineral prospectivity modeling (MPM). The northwestern portion of Ahar-Arasbaran porphyry copper belt (AAPCB) is situated within the Urumieh-Dokhtar magmatic belt (UDMB). Because of owning many worthwhile Cu-Mo and Cu-Au porphyry deposits, this area is entitled to incorporate diverse spatial evidence layers for the MPM. In this paper, a hybrid AHP-VIKOR, as an improved knowledge-driven MPM procedure has been proposed for integration of various exploration evidence layers. For this, the AHP is used to calculate important weights of spatial criteria while the VIKOR is applied to outline ultimate prospectivity model. Six effective spatial evidence layers pertaining to the Varzaghan District are selected: (1) multi-elemental geochemical layer of Cu-Mo-Bi-Au; (2) remotely sensed data of argillic, phyllic, and iron oxide alteration layers; and (3) geological and structural layers of Oligo-Miocene intrusions and fault. In addition, a fuzzy prospectivity model (γ?=?0.9) is implemented to assess the AHP-VIKOR approach. Two credible validation methods comprising normalized density index and success rate curve are adapted for quantitative evaluation of predictive models and enhancing the probability of exploration success. The achieved results proved the higher accuracy of the AHP-VIKOR model compared with the fuzzy model in delimiting the favorable areas.     

Mapping mineral prospectivity for Cu polymetallic mineralization in southwest Fujian Province,China

In this study, both the fuzzy weights of evidence (FWofE) and random forest (RF) methods were applied to map the mineral prospectivity for Cu polymetallic mineralization in southwestern Fujian Province, which is an important Cu polymetallic belt in China. Recent studies have revealed that the Zijinshan porphyry–epithermal Cu deposit is associated with Jurassic to Cretaceous (Yanshanian) intermediate to felsic intrusions and faulting tectonics. Evidence layers, which are key indicators of the formation of Zijinshan porphyry–epithermal Cu mineralization, include: (1) Jurassic to Cretaceous intermediate–felsic intrusions; (2) mineralization-related geochemical anomalies; (3) faults; and (4) Jurassic to Cretaceous volcanic rocks. These layers were determined using spatial analyses in support by GeoDAS and ArcGIS based on geological, geochemical, and geophysical data. The results demonstrated that most of the known Cu occurrences are in areas linked to high probability values. The target areas delineated by the FWofE occupy 10% of the study region and contain 60% of the total number of known Cu occurrences. In comparison with FWofE, the resulting RF areas occupy 15% of the study area, but contain 90% of the total number of known Cu occurrences. The normalized density value of 1.66 for RF is higher than the 1.15 value for FWofE, indicating that RF performs better than FWofE. Receiver operating characteristics (ROC) were used to validate the prospectivity model and check the effects of overfitting. The area under the ROC curve (AUC) was greater than 0.5, indicating that both prospectivity maps are useful in Cu polymetallic prospectivity mapping in southwestern Fujian Province.     

The use of the weights-of-evidence modeling technique to predictive porphyry Cu potential mapping in Ahar–Arasbaran zone,Iran

The weights-of-evidence is a data-driven method that provides a simple approach to integration of diverse geo-data set information. In this study, we will use weights-of-evidence to build a model for predicting tracts in the Ahar–Arasbaran zone of Urumieh-Dokhtar orogenic belt (northwestern Iran) that are favorable for porphyry copper deposits. Weights of evidence are a data-driven method requiring known deposits and occurrences that are used as training points in the evaluated area. This zone hosts two major porphyry Cu deposits (The Sarcheshmeh deposit contains 450 million tonnes of sulfide ore with an average grade of 1.13 % Cu and 0.03 % Mo and Sungun deposit, which has 500 million tonnes of sulfide reserves grading 0.76 % Cu and 0.01 % Mo), and a number of subeconomic porphyry copper deposits are all associated with Mid- to Late Miocene diorite/granodiorite to quartz-monzonite stocks. Five evidential layers including geology, alteration, geochemistry, geophysics, and faulting are chosen for potential mapping. Weight factors were determined based on the applied method to generate last mineral prospectivity map. The studied area reduces to less than 11.78 %, while large zones are excluded for further studies. This result represents a significant area reduction and may help to better focus on mineral exploration targeting porphyry copper deposits in the Ahar–Arasbaran zone.     

Data-driven predictive mapping of gold prospectivity,Baguio district,Philippines: Application of Random Forests algorithm

The Random Forests (RF) algorithm has recently become a fledgling method for data-driven predictive mapping of mineral prospectivity, and so it is instructive to further study its efficacy in this particular field. This study, carried out using Baguio gold district (Philippines), examines (a) the sensitivity of the RF algorithm to different sets of deposit and non-deposit locations as training data and (b) the performance of RF modeling compared to established methods for data-driven predictive mapping of mineral prospectivity. We found that RF modeling with different training sets of deposit/non-deposit locations is stable and reproducible, and it accurately captures the spatial relationships between the predictor variables and the training deposit/non-deposit locations. For data-driven predictive mapping of epithermal Au prospectivity in the Baguio district, we found that (a) the success-rates of RF modeling are superior to those of weights-of-evidence, evidential belief and logistic regression modeling and (b) the prediction-rate of RF modeling is superior to that of weights-of-evidence modeling but approximately equal to those of evidential belief and logistic regression modeling. Therefore, the RF algorithm is potentially much more useful than existing methods that are currently used for data-driven predictive mapping of mineral prospectivity. However, further testing of the method in other areas is needed to fully explore its usefulness in data-driven predictive mapping of mineral prospectivity.     

Fuzzy logic mineral potential mapping for copper exploration using multi-disciplinary geo-datasets,a case study in seridune deposit,Iran

This paper describes the application of the knowledge-based fuzzy logic method to integrate various exploratory geo-dataset in order to prepare a mineral prospectivity map (MPM) for copper exploration. Different geophysical layers which are derived from the magnetic and the electrical surveys, along with the ones extracted from the background geology (i.e., lithology, fault and alteration) and geochemical data are incorporated in such process. Seridune copper deposit located in the Kerman province of Iran is the case study to delineate its high potential zones of Cu-bearing mineralization for drilling additional boreholes. Four layers from the magnetic data involving upward continuation, analytic signal, reduced to pole and pseudo gravity are assigned in the multi-disciplinary geo-dataset to locate the intrusive complexes responsible for Cu mineralization. The apparent resistivity, chargeability and sulfide factor layers acquired from geo-electrical data are also included in the final preparation of MPM. Then the normalized weights of seven geophysical, three geological and one geochemical evidential layers as main criteria are determined based upon the knowledge of expert decision makers. Fuzzy operators (i.e., Sum and Gamma) are applied to integrate these exploratory features. To evaluate the performance and applicability of the approach, the productivity of the drilled boreholes (Cu concentration multiplied by ore thickness) are used to validate the produced MPMs. It is shown that an optimum correlation coefficient of 0.86 exists between the MPM values and Cu productivity criterion along drilled boreholes.     

Prospectivity for epithermal gold–silver deposits in the Deseado Massif,Argentina

Previous prospectivity modelling for epithermal Au–Ag deposits in the Deseado Massif, southern Argentina, provided regional-scale prospectivity maps that were of limited help in guiding exploration activities within districts or smaller areas, because of their low level of detail. Because several districts in the Deseado Massif still need to be explored, prospectivity maps produced with higher detail would be more helpful for exploration in this region.We mapped prospectivity for low- and intermediate-sulfidation epithermal deposits (LISEDs) in the Deseado Massif at both regional and district scales, producing two different prospectivity models, one at regional scale and the other at district-scale. The models were obtained from two datasets of geological evidence layers by the weights-of-evidence (WofE) method. We used more deposits than in previous studies, and we applied the leave-one-out cross validation (LOOCV) method, which allowed using all deposits for training and validating the models. To ensure statistical robustness, the regional and district-scale models were selected amongst six combinations of geological evidence layers based on results from conditional independence tests.The regional-scale model (1000 m spatial resolution), was generated with readily available data, including a lithological layer with limited detail and accuracy, a clay alteration layer derived from a Landsat 5/7 band ratio, and a map of proximity to regional-scale structures. The district-scale model (100 m spatial resolution) was generated from evidence layers that were more detailed, accurate and diverse than the regional-scale layers. They were also more cumbersome to process and combine to cover large areas. The evidence layers included clay alteration and silica abundance derived from ASTER data, and a map of lineament densities. The use of these evidence layers was restricted to areas of favourable lithologies, which were derived from a geological map of higher detail and accuracy than the one used for the regional-scale prospectivity mapping.The two prospectivity models were compared and their suitability for prediction of the prospectivity in the district-scale area was determined. During the modelling process, the spatial association of the different types of evidence and the mineral deposits were calculated. Based on these results the relative importance of the different evidence layers could be determined. It could be inferred which type of geological evidence could potentially improve the modelling results by additional investigation and better representation.We conclude that prospectivity mapping for LISEDs at regional and district-scales were successfully carried out by using WofE and LOOCV methods. Our regional-scale prospectivity model was better than previous prospectivity models of the Deseado Massif. Our district-scale prospectivity model showed to be more effective, reliable and useful than the regional-scale model for mapping at district level. This resulted from the use of higher resolution evidential layers, higher detail and accuracy of the geological maps, and the application of ASTER data instead of Landsat ETM + data. District-scale prospectivity mapping could be further improved by: a) a more accurate determination of the age of mineralization relative to that of lithological units in the districts; b) more accurate and detailed mapping of the favourable units than what is currently available; c) a better understanding of the relationships between LISEDs and the geological evidence used in this research, in particular the relationship with hydrothermal clay alteration, and the method of detection of the clay minerals; and d) inclusion of other data layers, such as geochemistry and geophysics, that have not been used in this study.     

Data fusion and porphyry copper prospectivity models,southeastern Arizona

Mineral exploration programs commonly use a combination of geological, geophysical and remotely sensed data to detect sets of optimal conditions for potential ore deposits. Prospectivity mapping techniques can integrate and analyse these digital geological data sets to produce maps that identify where optimal conditions converge. Three prospectivity mapping techniques – weights of evidence, fuzzy logic and a combination of these two methods – were applied to a 32,000 km² study area within the southeastern Arizona porphyry Cu district and then assessed based on their ability to identify new and existing areas of high mineral prospectivity. Validity testing revealed that the fuzzy logic method using membership values based on an exploration model identified known Cu deposits considerably better than those that relied solely on weights of evidence, and slightly better than those that used a combination of weights of evidence and fuzzy logic. This led to the selection of the prospectivity map created using the fuzzy logic method with membership values based on an exploration model. Three case study areas were identified that comprise many critical geological and geophysical characteristics favourable to hosting porphyry Cu mineralisation, but not associated with known mining or exploration activity. Detailed analysis of each case study has been performed to promote these areas as potential targets and to demonstrate the ability of prospectivity modelling techniques as useful tools in mineral exploration programs.     

An early Cretaceous analogue of the ~ 2.5 Ga Malanjkhand porphyry Cu deposit,Central India

The ~ 2.5 Ga Malanjkhand Cu mineralization is hosted by adakitic granitoids in central India. The mineralization represents a large Cu deposit. However, significant debate still surrounds its identification as an analogue of modern circum-Pacific style porphyry Cu deposits. The controversy is intricately linked to several first-order geological issues, such as: the onset of modern plate tectonics and ensuing supercontinent cycles, temporal evolution of the Earth's continental crust coupled with buoyancy of the sub-continental lithospheric mantle (SCLM) and oxidation state of the sub-arc mantle wedge. The petrology and geochemistry of the early Cretaceous Lower Yangtze River Belt (LYRB) adakitic granitoids, central-eastern China that hosts several porphyry Cu deposits are similar to the ~ 2.5 Ga Malanjkhand adakitic granitoids of central India, hosting Cu mineralization. The relict amphibole chemistry of both, the LYRB and Malanjkhand granitoids reveals similar “porphyry mineralizing trends” implying high concentrations of H₂O and elevated fO₂ conditions of the ore-bearing shallowly emplaced adakitic granitoids. Consequently, the Malanjkhand and LYRB adakitic granitoids were generated in near-identical tectonothermal regimes. The LYRB porphyry Cu deposits belong to the circum–Pacific metallogenic belt of the Eurasian active continental margin. Collectively, the mineralogical, petrological and geochemical similarities of the Malanjkhand and the LYRB adakitic granitoids imply porphyry style mineralization of the Malanjkhand Cu deposit. The identification of Malanjkhand mineralization as a truly Neoarchean porphyry Cu deposit along with coeval adakites, calc-alkaline rhyolites, high-Mg andesites (HMA), followed by rift-related tholeiites and A₂-type granites helps to constrain the tectonic evolution of central India. The rarity of porphyry Cu deposits in the Earth's early history is primarily attributed to their lack of preservation. This study opens up exploration possibilities for hitherto unexplored and concealed porphyry Cu deposits in other geologically favorable Precambrian terranes comprising shallowly emplaced adakitic granitoids.     

Selection of coherent deposit-type locations and their application in data-driven mineral prospectivity mapping

Data-driven prospectivity mapping can be undermined by dissimilarity in multivariate spatial data signatures of deposit-type locations. Most cases of data-driven prospectivity mapping, however, make use of training sets of randomly selected deposit-type locations with the implicit assumption that they are coherent (i.e., with similar multivariate spatial data signatures). This study shows that the quality of data-driven prospectivity mapping can be improved by using a training set of coherent deposit-type locations. Analysis and selection of coherent deposit-type locations was performed via logistic regression, by using multiple sets of deposit occurrence favourability scores of univariate geoscience spatial data as independent variables and binary deposit occurrence scores as dependent variable. The set of coherent deposit-type locations and three sets of randomly selected deposit-type locations were each used in data-driven prospectivity mapping via application of evidential belief functions. The prospectivity map based on the training set of coherent deposit-type locations resulted in lower uncertainty, better goodness-of-fit to the training set, and better predictive capacity against a cross-validation set of economic deposits of the type sought. This study shows that explicit selection of training set of coherent deposit-type locations should be applied in data-driven prospectivity mapping.     

A comprehensive VIKOR method for integration of various exploratory data in mineral potential mapping

The central Iranian volcanic-sedimentary belt in Kerman province of Iran that is located within the Urumieh-Dokhtar magmatic arc zone is chosen to integrate diverse evidential layers for mineral potential mapping. The studied area has high potential of mineral occurrences especially porphyry copper, and the prepared potential maps aim to outline new prospect zones for further investigation. Two evidential layers including the downward continued map and the analytic signal of filtered magnetic data are generated to be used as geophysical plausible traces of porphyry copper occurrences. The low values of the resistivity layer acquired from airborne frequency domain electromagnetic data are also used as an electrical criterion in this study. Four remote sensing evidential layers including argillic, phyllic, propylitic, and hydroxyl alterations are extracted from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images in order to map the altered areas associated with porphyry copper deposits. The Enhanced Thematic Mapper Plus (ETM+) images are used as well to prepare iron oxide layer. Since potassic alteration is generally the mainstay of copper ore mineralization, the airborne potassium radiometry data is used to explore both phyllic and potassic alteration. Finally, the geochemical layers of Cu/B/Pb/Zn elements and the main geochemical component responsible for ore mineralization extracted from principal component analysis are included in the integration process to prepare final potential maps. The conventional and the extended version of VIKOR method (as a well-known algorithm in multi-criteria decision making problems) produced two mineral potential maps, and the results were compared with the ones acquired from prevalent methods of the index overlay and fuzzy logic operators of sum and gamma. The final mineral potential maps based upon desired geo-data set indicate adequately matching of high potential zones with previous working and active mines of copper deposits.     

Evolution of magmatic-hydrothermal system of the Kalaxiange’er porphyry copper belt and implications for ore formation (Xinjiang,China)

The Kalaxiange’er porphyry copper ore belt is situated in the eastern part of the southern Altai of the Central Asian Orogenic Belt and forms part of a broad zone of Cu porphyry mineralization in southern Mongolia, which includes the Oyu Tolgoi ore district and other copper–gold deposits. The copper ore bodies are spatially associated with porphyry intrusions of granodiorite, quartz diorite, quartz syenite, and quartz monzonite and have a polygenetic (polychromous) origin (magmatic porphyry, hydrothermal, and supergene). The mineralized porphyries are characterized by almost identical REE and trace element patterns. The Zr/Hf and Nb/Ta ratios are similar to those of normal granite produced through the evolution of mantle magma. The low initial Sr isotope ratio I_Sr, varying within a narrow range of values (0.703790–0.704218), corresponds to that of primitive mantle, whereas the εNd(T) value of porphyry varies from 5.8 to 8.4 and is similar to that of MORB. These data testify to the upper-mantle genesis of the parental magmas of ore-bearing porphyry, which were then contaminated with crustal material in an island-arc environment. The isotopic composition of sulfur (unimodal distribution of δ34S with peak values of − 2 to − 4‰) evidences its deep magmatic origin; the few lower negative δ³⁴S values suggest that part of S was extracted from volcanic deposits later. The isotopic characteristics of Pb testify to its mixed crust–upper-mantle origin. According to SHRIMP U–Pb geochronological data for zircon from granite porphyry and granodiorite porphyry, mineralization at the Xiletekehalasu porphyry Cu deposit formed in two stages: (1) Hercynian “porphyry” stage (375.2 ± 8.7 Ma), expressed as the formation of porphyry with disseminated and vein–disseminated mineralization, and (2) Indosinian stage (217.9 ± 4.2 Ma), expressed as superposed hydrothermal mineralization. The Re–Os isotope data on molybdenite (376.9 ± 2.2 Ma) are the most consistent with the age of primary mineralization at the Xiletekehalasu porphyry Cu deposit, whereas the Ar–Ar isotopic age (230 ± 5 Ma) of K-feldspar–quartz vein corresponds to the stage of hydrothermal mineralization. The results show that mineralization at the Xiletekehalasu porphyry Cu deposit was a multistage process which resulted in the superposition of the Indosinian hydrothermal mineralization on the Hercynian porphyry Cu mineralization.     

Petrogenesis and metallogenic setting of porphyries of the Duobuza porphyry Cu–Au deposit,central Tibet,China

Given that the Duobuza deposit was the first porphyry Cu–Au deposit discovered in central Tibet, the mineralization and mineralized porphyry in this area have been the focus of intensive research, yet the overall porphyry sequence associated with the deposit remains poorly understood. New geological mapping, logging, and sampling of an early granodiorite porphyry, an inter-mineralization porphyry, and a late-mineralization diorite porphyry were complemented by LA–ICP–MS zircon dating, whole-rock geochemical and Sr–Nd isotopic analyses, and in situ Hf isotopic analyses for both inter- and late-mineralization porphyry intrusions. All of the porphyry intrusions are high-K and calc-alkaline, and were emplaced at ca. 120 Ma. The geochemistry of these intrusions is indicative of arc magmatism, as all three porphyry phases are enriched in light rare earth elements and large ion lithophile elements, and depleted in heavy rare earth elements and high field strength elements. These similar characteristics of the intrusions, when combined with the relatively high (⁸⁷Sr/⁸⁶Sr)_i, negative ε_Nd(t), and positive ε_Hf(t) values, suggest that the magmas that formed the porphyries were derived from a common source region and shared a single magma chamber. The magmas were generated by the mixing of upwelling metasomatized mantle-wedge-derived mafic magmas and magmas generated by partial melting of amphibolite within the lower crust.The inter-mineralization porphyry has the lowest ε_Nd(t) and highest (⁸⁷Sr/⁸⁶Sr)_i values, suggesting that a large amount of lower-crust-derived material was incorporated into the melt and that metals such as Cu and Au from the enriched lower crust were scavenged by the parental magma. The relative mafic late-mineralization diorite porphyry phase was formed by the residual magma in the magma chamber mixing with upwelling mafic melt derived from metasomatized mantle. The magmatic–hydrothermal evolution of the magma in the chamber released ore-forming fluid that was transported mainly by the inter-mineralization porphyry phase during the mineralization stage, which ultimately formed the Duobuza porphyry Cu–Au deposit.These porphyritic intrusions of the Duobuza deposit have high Mg^# and low (La/Yb)_N values, and show some high LILE/HFSE ratios, indicating the magma source was enriched by interaction with slab-derived fluids. Combined with age constraints on the regional tectonic evolution, these dating and geochemical results suggest that the Duobuza porphyry Cu–Au deposit formed in a subduction setting during the final stages of the northward subduction of the Neo-Tethyan Ocean.     

Porphyry,epithermal, and orogenic gold prospectivity of Argentina

This paper presents a review of the available information on the significant porphyry, epithermal, and orogenic gold districts in Argentina, including the tectonic, geological, and structural settings of large deposits or deposits that have been exploited in the past. Based on this review of the geology and mineralization, targeting models are developed for epithermal and orogenic gold systems, in order to produce GIS-based prospectivity models. Using publically available digital geoscience data, weights of evidence and fuzzy logic prospectivity maps were generated for epithermal and orogenic gold mineralization in Argentina. The results of the prospectivity mapping highlight existing gold deposits within known mineralized districts throughout Argentina, as well as other highly prospective areas with no known deposits within these districts. Additionally, areas within Argentina that have no known gold mineralization (based on publically available information) were highlighted as being highly prospective based on the models used.     

Ages and petrogenesis of the late Triassic andesitic rocks at the Luerma porphyry Cu deposit,western Gangdese,and implications for regional metallogeny

The Tibetan Plateau is one of the most significant Cu poly-metallic mineralization regions in the world and preserves important information related to subductional and collisional porphyry Cu mineralization. This study investigates a new occurrence of Cu mineralization-related andesitic porphyries in the western domain of the Gangdese magmatic belt and assesses its petrologic, zircon U-Pb geochronology, whole-rock chemistry, and Sr-Nd-Hf-Pb isotope data. Zircon U-Pb dating of three ore-related porphyries yields crystallization ages of 212–211 Ma. These ages are consistent with previous molybdenite Re-Os dating, indicating a late Triassic magmatic and Cu mineralization event in the western Gangdese magmatic belt. Nb, Ta, and Ti depletion, Th and LREE enrichment, and high La/Yb and Th/Yb ratios in addition to high U/Yb ratios from zircons suggest that the magma was generated in an active continental arc setting. The porphyries have radiogenic isotopic compositions with (⁸⁷Sr/⁸⁶Sr)_i 0.70431–0.70473, ε_Nd(t) +1.1 to +3.8, (²⁰⁷Pb^/204Pb)_i 15.601–15.622, and (²⁰⁸Pb/²⁰⁴Pb)_i 38.450–38.693, as well as high positive zircon ε_Hf(t) values from +6.2 to +10.6 (mean value 8.3), corresponding to model ages (T_DM) ranging from 509 Ma to 819 Ma (mean 646 Ma). This suggests that the andesitic magmatism was dominantly sourced from depleted mantle materials that were modified by subducted oceanic sediment-derived melts during the subduction of the Neo-Tethys Ocean. The mineralization-related porphyries contain amphibole and epidote, as well as high whole-rock Fe₂O₃/FeO and zircon Ce⁴⁺/Ce³⁺ ratios, suggesting hydrous and highly oxidized parent magmas. Considering the existing Cu mineralization and highly oxidized magma of the well-preserved Triassic andesitic igneous rocks in the western Gangdese belt, the subduction-related continental arc magma system is favorable for subduction-related porphyry Cu deposits. The existence of Luerma porphyry mineralization demonstrates that there are at least five generations of porphyry Cu-(Mo-Au) mineralization in the Gangdese magmatic belt, which advances the timeframe of porphyry mineralization to the late Triassic.     

From Predictive Mapping of Mineral Prospectivity to Quantitative Estimation of Number of Undiscovered Prospects

This paper proposes that the spatial pattern of known prospects of the deposit‐type sought is the key to link predictive mapping of mineral prospectivity (PMMP) and quantitative mineral resource assessment (QMRA). This proposition is demonstrated by PMMP for hydrothermal Au‐Cu deposits (HACD) and by estimating the number of undiscovered prospects for HACD in Catanduanes Island (Philippines). The results of analyses of the spatial pattern of known prospects of HACD and their spatial associations with geological features are consistent with existing knowledge of geological controls on hydrothermal Au‐Cu mineralization in the island and elsewhere, and are used to define spatial recognition criteria of regional‐scale prospectivity for HACD. Integration of layers of evidence representing the spatial recognition criteria of prospectivity via application of data‐driven evidential belief functions results in a map of prospective areas occupying 20% of the island with fitting‐ and prediction‐rates of 76% and 70%, respectively. The predictive map of prospective areas and a proxy measure for degrees of exploration based on the spatial pattern of known prospects of HACD were used in one‐level prediction of undiscovered mineral endowment, which yielded estimates of 79 to 112 undiscovered prospects of HACD. Application of radial‐density fractal analysis of the spatial pattern of known prospects of HACD results in an estimate of 113 undiscovered prospects of HACD. Thus, the results of the study support the proposition that PMMP can be a part of QMRA if the spatial pattern of discovered prospects of the deposit‐type sought is considered in both PMMP and QMRA.     

Geochronology and geochemistry of the Wunugetushan porphyry Cu–Mo deposit in NE china,and their geological significance

The Wunugetushan porphyry Cu–Mo deposit is located in the Manzhouli district of NE China, on the southern margin of the Mesozoic Mongol–Okhotsk Orogenic Belt. Concentric rings of hydrothermal alteration and Cu–Mo mineralization surround an Early–Middle Jurassic monzogranitic porphyry. The Cu–Mo mineralization is clearly related to the quartz–potassic and quartz–sericite alteration. Molybdenite Re–Os and groundmass ⁴⁰Ar/³⁹Ar of the host porphyry dates indicate that the ore-formation and porphyry-emplacement occurred at 177.6 ± 4.5 Ma and 179.0 ± 1.9 Ma, respectively. Geochemically, the host porphyry of the deposit is characterized by strong LREE/HREE fractionation, enrichment in LILE, Ba, Rb, U, Th and Pb, and depletion of HFSE, Nb, Ta, Ti and HREE. The Sr–Nd–Pb isotopic compositions of the porphyry display an varied initial (⁸⁷Sr/⁸⁶Sr)_i ratio, a positive ε_Nd(t) values and high ²⁰⁶Pb/²⁰⁴Pb_t, ²⁰⁷Pb/²⁰⁴Pb_t and ²⁰⁸Pb/²⁰⁴Pb_t ratios. These data indicate that the magmatic source of the host porphyry comprised two end-members: lithospheric mantle metasomatized by fluids derived from the subducted slab; and continental crust. We infer that the primitive magma of the host porphyry was derived from crust–mantle transition zone. Based on regional geology and geochemistry of the host porphyry, the Wunugetushan deposit is suggested to form in a continental collision environment after closure of the Mongol–Okhotsk Ocean.     

U–Pb dating,geochemistry, and Sr–Nd isotopic composition of a granodiorite porphyry from the Jiadanggen Cu–(Mo) deposit in the Eastern Kunlun metallogenic belt,Qinghai Province,China

The Jiadanggen porphyry Cu–(Mo) deposit is newly discovered and located in the Eastern Kunlun metallogenic belt of Qinghai Province, China. Here, we present a detailed study of the petrogenesis, magma source, and tectonic setting of the mineralization causative granodiorite porphyry. The new data indicate that the granodiorite porphyry is characterized by high SiO₂ (68.21–70.41 wt.%) and Al₂O₃, relatively high K₂O, low Na₂O, and low MgO and CaO concentrations, and is high-K calc-alkaline and peraluminous. The granodiorite porphyry has low Mg^# (38–46) values that are indicative of no interaction between the magmas and the mantle. The samples that we have examined have low Nb/Ta (9.17–10.3) and Rb/Sr (0.28–0.39) ratios, which are indicative of crustal-derived magmas. Source region discrimination diagrams indicate that the magmas that formed the granodiorite porphyry were derived from melting of a mixed amphibolite source in the lower crust. The samples have I_Sr values of 0.70954–0.70979, ε_Nd(t) values of − 8.3 to − 7.9, and t_2DM ages ranging from 1644 to 1677 Ma. These indicate that the magmas that formed this intrusion were generated by melting of Mesoproterozoic lower crustal material. Higher K(Rb) contents of the samples indicate that the magma source is high potassium basaltic material in the lower crust, which could be derived from an enriched mantle source. LA-ICP-MS zircon U–Pb dating of the granodiorite porphyry yields a late Indosinian age (concordia age of 227 ± 1 Ma; MSWD = 0.31), which is close to the molybdenite Re–Os isochron age (227.2 ± 1.9 Ma), indicating further the close relationship between the granodiorite porphyry and the Cu–(Mo) mineralization. These samples are LREE and LILE (e.g., Rb, K, Ba, and Sr) enriched, and HFSE (e.g., Nb, Ta, P, and Ti) depleted, especially in P and Ti, similar to the characteristics of volcanic arc magmas. This intrusion most likely formed during the later stage of Indosinian deep subduction of oceanic slab. This was associated with underplating of mantle-derived magmas, which provided heat for crustal melting. Similar to the Jiadanggen granodiorite porphyry, Indosinian hypabyssal intermediate-felsic intrusive rocks, formed under subduction tectonism or a transitional regime from subduction to syn-collision, make up the most important targets for porphyry Cu(Mo) deposits in the Eastern Kunlun metallogenic belt.     

Geochemical Characteristics and Zonation of Primary Halos of Pulang Porphyry Copper Deposit,Northwestern Yunnan Province,Southwestern China

The Pulang (普朗) porphyry copper deposit, located in the southern segment of the Yidun-Zhongdian (义敦-为中甸) island arc ore-forming belt of the Tethys-Himalaya ore-forming domain, is a recently discovered large copper deposit. Compared with the composition of granodiorite in China, the porphyry rocks in this area are enriched in W, Mo, Cu, Au, As, Sb, F, V, and Na2O (K1≥1.2). Compared with the composition of fresh porphyry rocks in this district, the mineralized rocks are enriched in Cn, Au, Ag, Mo, Pb, Zn, W, As, Sb, and K2O (K≥1.2). Some elements show clear anomalies, such as Zn, Ag, Cu, Au, W, and Mo, and can be regarded as pathfinders for prospecting new ore bodies in depth. It has been inferred from factor analysis that the Pulang porphyry copper deposit may have undergone the multiple stages of alteration and mineralization: (a) Cu-Au mineralization; (b) W-Mo mineralization; and (c) silicification and potassic metasomatism in the whole ore-forming process. A detailed zonation sequence of indicator elements is obtained using the variability index of indicator elements as follows: Zn→Ag→Cu→Au→W→Mo. According to this zonation, an index such as (Ag×Zn) D/(Mo×W) D can be constructed and regarded as a significant criterion for predicting the Cu potential at a particular depth.     

Predictive mapping of prospectivity for orogenic gold,Giyani greenstone belt (South Africa)

We present a mineral systems approach to predictive mapping of orogenic gold prospectivity in the Giyani greenstone belt (GGB) by using layers of spatial evidence representing district-scale processes that are critical to orogenic gold mineralization, namely (a) source of metals/fluids, (b) active pathways, (c) drivers of fluid flow and (d) metal deposition. To demonstrate that the quality of a predictive map of mineral prospectivity is a function of the quality of the maps used as sources of spatial evidence, we created two sets of prospectivity maps — one using an old lithologic map and another using an updated lithological map as two separate sources of spatial evidence for source of metals/fluids, drivers of fluid flow and metal deposition. We also demonstrate the importance of using spatially-coherent (or geologically-consistent) deposit occurrences in data-driven predictive mapping of mineral prospectivity. The best predictive orogenic gold prospectivity map obtained in this study is the one that made use of spatial evidence from the updated lithological map and spatially-coherent orogenic gold occurrences. This map predicts 20% of the GGB to be prospective for orogenic gold, with 89% goodness-of-fit between spatially-coherent inactive orogenic gold mines and individual layers of spatial evidence and 89% prediction-rate against spatially-coherent orogenic gold prospects. In comparison, the predictive gold prospectivity map obtained by using spatial evidence from the old lithological map and all gold occurrences has 80% goodness-of-fit but only 63% prediction-rate. These results mean that the prospectivity map based on spatially-coherent gold occurrences and spatial evidence from the updated lithological map predicts exploration targets better (i.e., 28% smaller prospective areas with 9% stronger fit to training gold mines and 26% higher prediction-rate with respect to validation gold prospects) than the prospectivity map based on all known gold occurrences and spatial evidence from the old lithological map.     

High oxidation magmatic evolution in the Naruo porphyry Cu deposit,Tibet, China

The Naruo porphyry Cu deposit is the third largest deposit discovered in the Duolong metallogenic district. Previous research has focused mainly on the geochemistry of the ore-bearing granodiorite porphyry; the metallogenesis remains poorly understood. In the present work, on the basis of outcrops and drilling core geological mapping, phases of early mineralization diorite, two inter-mineralization granodiorite porphyries, and late-mineralization granodiorite porphyry have been distinguished. Furthermore, the alteration zones were outlined, and the vein sequence was identified. The diorite and three porphyry phases were subjected to Laser Ablation Inductively Coupled Plasma Mass Spectrometry (La–ICP–MS) zircon U–Pb dating and in situ Hf isotope analyses as well as bulk major element, trace element, and Sr–Nd isotopic analyses. Molybdenite Re–Os dating was also conducted.The zircon U–Pb dating results show that the diorite and porphyry intrusions were emplaced at about 120 Ma, and the molybdenite Re–Os isochron age is 118.8 ± 1.9 Ma; this indicates that the Naruo porphyry Cu deposit was formed during a continuous magmatic–hydrothermal process. All of the diorite and granodiorite porphyry samples showed arc magmatic characteristics. Moreover, the moderate (⁸⁷Sr/⁸⁶Sr)_i ratios and low ε_Nd(t) and ε_Hf(t) values of the diorite and porphyry intrusions suggest the source region of the juvenile lower crust. The lower (⁸⁷Sr/⁸⁶Sr)_i and (¹⁴³Nd/¹⁴⁴Nd)_i ratios and higher ε_Nd(t) values and incompatible element concentrations than those in the granodiorite porphyry samples indicate a two-stage magmatic generation process for the intrusions. The early mineralization diorite has a high Cu concentration, implying that the source is enriched in Cu. However, the slightly lower Cu content of the late-mineralization granodiorite porphyry samples might imply Cu release from magmas and deposition within the metallogenic stage. The multiple stages of intrusions and subsequent volcanism within the Duolong metallogenic district, together with high Sr/Y features, indicate persistent magmatism during the metallogenic epoch, which is necessary for maintaining the activity of magmatic–hydrothermal and mineralization processes. Thus, the high Cu content in the source region, mantle-derived melt upwelling, and multiple stages of persistent magmatism were favorable for the formation of the Naruo porphyry Cu deposit.The high Fe₂O₃/FeO ratios of the diorite and granodiorite porphyry intrusions show very high oxidation features, which is coincident with estimated magmatic oxidation state calculated by the zircon trace element compositions. The high oxidation facilitates sulfur and chalcophile metals to be scavenged into the magmatic–hydrothermal systems, which is crucial for the metallogenesis of the Naruo porphyry Cu deposit.