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.
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•Mineralization in Kuh-Panj occurred in a Miocene granodiorite stock that intruded Eocene volcanic host rocks.•Alteration zoning pattern and vein paragenesis are similar to porphyry Cu deposits elsewhere.•Geochemical features of the Kuh-Panj system are similar to those of fertile porphyries.•The zircon 206Pb/238U ages of the porphyry stock ranging from 7.7 to 9.7 Ma (ave. 8.57 ± 0.49 Ma).•The Kuh-Panj deposit is classified as continental arc-related porphyry copper deposit.
Geochemical anomaly detection is an important issue in mineral exploration. The availability of a training dataset consisting of labeled geochemical samples of background and anomaly classes enables ...us to define a supervised pattern recognition framework for geochemical anomaly detection. Therefore, various classification and feature selection algorithms can be utilized to build a predictive model and classify the unseen geochemical samples into the pre-defined anomaly and background classes. In this study, some of the state-of-art feature selection and classification algorithms were utilized for supervised anomaly detection in the Kuh Panj porphyry-Cu district. Filter, wrapper and embedded mode feature selection algorithms were used to remove redundant and irrelevant elements from the classification procedure. Subsequently, AdaBoost (ADB), support vector machine (SVM) and Random Forest (RF) algorithms were trained with borehole and surface rock samples from the drilled parts of the study area to create a classified map depicting anomalous areas in the undrilled parts of the district. Results show that feature selection algorithms could play an important role in increasing the accuracy and generalization ability of the classifiers used. Wrapper mode subset selection method combined with a genetic algorithm (GA) search method resulted in the best performance in the study area. Applied classification algorithms outperform Gaussian linear discriminant analysis (GLDA) and provide more accurate, robust and reliable results. Among the applied classification methods, ADB achieved the best leave-one-out cross-validation (LOO) error rate of 0.06. Meanwhile, comparison of the resulted classified map using ADB with another one created via concentration–area fractal model indicated advantage of the former one in terms of detecting high-promising prospective target areas in the study region.
•The concept of supervised geochemical pattern recognition was introduced.•Surficial and subsurface data were used to detect geochemical anomalies.•The state-of-art classification algorithms were utilized for anomaly detection.•Feature selection algorithms were integrated to the anomaly detection.
The Kerman Cenozoic magmatic arc (KCMA), located on the southeast of the Central Iranian volcano-plutonic belt, hosts some world class porphyry copper deposits. Temporally, the deposits overlap with ...the Alpine–Himalayan collision, which has some key implications for the existence or lack of copper mineralization during orogenic arc system development. Transition from normal calc-alkaline arc magmatism in the Eocene-Oligocene (Jebal Barez-type) to adakite-like calc-alkaline magmatism (Kuh Panj-type) in the mid-late Miocene-Pliocene reflects the onset of collision between the Afro-Arabian and Eurasian plates in the Kerman Cenozoic arc segment. The aim of this review is to determine the role of Cenozoic magmatic events in the development of economic to sub-economic porphyry copper mineralization in the southeastern parts of the Central Iranian volcano-plutonic belt. In order to discriminate between the various magmatic systems (KCMA) involved in that development, a geochemical investigation is carried out using samples collected from all important deposits in the region (this study) and previous published data by earlier researchers in this region. It is evident from these data that the collisional Neogene Kuh Panj porphyry suite is distinctly more evolved than the pre-collisional Eocene-Oligocene Jebal Barez granitoids, with relative enrichments in incompatible elements, Sr/Y (>55), and La/Yb (>20), slightly positive Eu anomalies (Eun/Eu*≈1), and depletions in HFSE, with La/Smn≈4.6–6.6 and Dy/Ybn≈1.0–2.0, and relatively non-radiogenic Sr isotope signatures (87Sr/86Sr=0.7042–0.7047). In contrast, Jebal Barez granitoids exhibit low Sr/Y (<21) and La/Yb (<9) ratios, negative Eu anomalies (Eun/Eu*≈0.5), and enrichment in HFSE and radiogenic Sr isotope signatures (87Sr/86Sr=0.7053–0.7075). The temporal along with lithogeochemical and isotopic changes, reflect a progressive transfer of the melting zone from the juvenile mafic lower crust (garnet–free amphibolite) into garnet–amphibolite. This transfer is the result of compressional stress along with tectonic shortening during Eocene-Oligocene (~30–35km crustal thickness) to mid-late Miocene (~45–55km thick or 12–15kbar). The absence of volcanism, under prevailing compressional conditions (mid-late Miocene-Pliocene), prevented the escape of SO2 from the adakite-like, sulfur-rich, highly oxidized magmas (“closed porphyry systems”), which allowed formation of several world-class to giant mineral deposits. Volcanic activity during formation of the subvolcanic Eocene-Oligocene porphyries allowed development of “open porphyry systems”, which, in turn to partial outgassing of volatiles, and therefore, far less significant mineral deposits.
•The hydrochemical facies of river water was dominated by Ca-HCO3 in Tajikistan.•Rivers from eastern Tajikistan presented more negative δ18O values.•A negative relationship between river water δ18O ...and elevation was observed.•Water quality at some sites poses safety concern for drinking and irrigation.
Water resources in Central Asia from the mountainous headwater catchments is changing due to the shrinkage of glaciers in the Tian Shan and Pamir mountain systems. In order to predict future changes in water quality, it is crucial to understand what factors are governing the spatial variations of water chemistry and hydrological processes in mountainous headwater catchments. In this study, water chemistry including major ions and stable isotopes in the headwaters of major Tajikistan rivers was studied. Results showed that Tajikistan river water had an alkaline pH value (mean: 8.2) and total dissolved solids (mean: 368.5mg/L) were higher than the global average value. Ca2+, Na+, HCO3−, and SO42− in the rivers were the most abundant cations and anions, controlled by the rock weathering process and evaporation-crystallization processes. The hydrochemical facies of river water was dominated by Ca-HCO3 (71.7%) and exhibited spatial heterogeneity, which was related to the lithologic compositions and water source across Tajikistan. A significant negative correlation of river water δ18O with elevation was observed with a vertical lapse rate of 0.17‰/100 m. The more negative δ18O values in rivers from eastern Tajikistan were scattered in the lower left corner of the δ18O-δ2H plot, implying that the rivers were primarily supplied by snow/glacier meltwater because of the substantial number of glaciers and high elevation mountain in eastern regions. The drinking and irrigation suitability from ionic compositions revealed that the water quality of Tajikistan rivers was naturally good, though some sites posed a safety concern. These findings can provide new insights into sustainable management of water quality in the climatically and lithologically distinct segments of headwater regions in the Tajikistan Pamirs.
Pre-collisional Eocene–Oligocene arc diorites, quartzdiorites, granodiorites, and volcanic equivalents in the Kerman arc segment in central Iran lack porphyry Cu mineralization and ore deposits, ...whereas collisional middle-late Miocene adakite-like porphyritic granodiorites without volcanic equivalents host some of the world’s largest Cu ore deposits. Petrological and structural constraints suggest a direct link between orogenic arc crust evolution and the presence of a fertile metallogenic environment. Ore-hosting Kuh Panj porphyry intrusions exhibit high Sr (>400 ppm), low Y (<12 ppm) contents, significant REE fractionation (La/Yb > 20), no negative Eu anomalies (Eu/Eu
*
≥ 1), and relatively non-radiogenic Sr isotope signatures (
87
Sr/
86
Sr = 0.7042–0.7047), relative to Eocene–Oligocene granitoids (mainly Sr < 400 ppm; Y > 12; La/Yb < 15; Eu/Eu
*
< 1;
87
Sr/
86
Sr = 0.7053–0.7068). Trace element modeling indicates peridotite melting for the barren Eocene–Oligocene intrusions and a hydrous garnet-bearing amphibolite source for middle-late Miocene ore-hosting intrusions. The presence of garnet implies collisional arc crustal thickening by shortening and basaltic underplating from about 30–35 to 40–45 km or 12 kbar. The changes in residual mineralogy in the source of Eocene to Miocene rocks in the Kerman arc segment reflect probing of a thickening arc crust by recycling melting of the arc crustal keel. Underplating of Cu and sulfur-rich melts from fertile peridotite generated a fertile metallogenic reservoir at or near the crust–mantle boundary, and dehydration melting under oxidizing conditions produced syn- and post-collisional ore-hosting intrusions, while the lack of post-collisional volcanism prevented the venting of volatiles to the atmosphere from sulfur-rich and oxidized adakitic magmas.
A common objective method for anomaly detection in geochemical exploration is target delineation by discriminant function analysis. Discriminant analysis (DA) is a multivariate statistical technique ...that classifies each observation into a specific group based on observed predictor variables and predefined groups. In the present study a new approach is considered for geochemical anomaly identification employing DA and “real” pre-defined “anomaly” and “background” data set. The anomalous and background samples are identified based on presence or absence of mineralization in depth; so, this method is introduced as “objective approach”. In order to classify surface geochemical samples into anomaly and background, assays of core drillings in the Kuh Panj porphyry Cu mineralization are used. They are classed as anomaly if the presence of mineralization is proven and are labeled as background if the absence of mineralization is confirmed in cores. Stepwise Linear discriminant analysis (LDA) and quadratic discriminant analysis (QDA) are utilized to achieve discrimination functions. For the test data used to generate the models, both LDA and QDA methods have led to perfect classification however cross validation has shown 84% and 74% total correct classification for LDA and QDA respectively. Outcomes of this research have demonstrated that LDA can effectively be employed as an objective method for geochemical anomaly identification if available information from geology and geochemistry of target area are employed and utilized. It is also shown that the definition of anomalism in geochemical exploration can be improved remarkably by this approach.
•Objective based geochemical anomaly detection is proposed for real anomaly identification.•Anomaly and background are defined based on presence or absence of mineralization in drill cores.•Linear discriminant analysis has successfully delineated the mineralized zones in the Kuh Panj porphyry copper deposit.•Linear discriminator has classified the samples more effectively than quadratic discriminator.
Cenozoic gneiss domes comprise one third of the surface exposure of the Pamir and provide a window into the deep crustal processes of the India‐Asia collision. The largest of these are the doubly ...vergent, composite Shakhdara‐Alichur domes of the southwestern Pamir, Tajikistan, and Afghanistan; they are separated by a low‐strain horst. Top‐to‐SSE, noncoaxial pervasive flow over the up to 4 km thick South Pamir shear zone exhumed crust from 30–40 km depth in the ~250 × 80 km Shakhdara dome; the top‐to‐NNE Alichur shear zone exposed upper crustal rocks in the ~125 × 25 km Alichur dome. The Gunt shear zone bounds the Shakhdara dome in the north and records alternations of normal shear and dextral transpression; it contributed little to bulk exhumation. Footwall exhumation along two low‐angle, normal‐sense detachments resulted in up to 90 km syn‐orogenic ~N‐S extension. Extension in the southwestern Pamir opposes shortening in a fold‐thrust belt north of the domes and in particular in the Tajik depression, where an evaporitic décollement facilitated upper crustal shortening. Gravitational collapse of the Pamir‐plateau margin drove core‐complex formation in the southwestern Pamir and shortening of the weak foreland adjacent to the plateau. Overall, this geometry defines a “vertical extrusion” scenario, comprising frontal and basal underthrusting and thickening, and hanging gravitationally driven normal shear. In contrast to the Himalayan vertical extrusion scenario, erosion in the Pamir was minor, preserving most of the extruded deep crust, including the top of the South Pamir shear zone at peak elevations throughout the dome.
Key Points
Giant Cenozoic migmatitic gneiss domes crop out in the southern Pamir
Mid‐crustal rocks were exhumed in the footwall of two low‐angle detachments
Exhumation was facilitated by the South Pamir and the Alichur shear zones
Newly developed approaches based on satellite altimetry and gravity measurements provide promising results on glacier dynamics in the Pamir‐Himalaya but cannot resolve short‐term natural variability ...at regional and finer scale. We contribute to the ongoing debate by upscaling a hydrological model that we calibrated for the central Pamir. The model resolves the spatiotemporal variability in runoff over the entire catchment domain with high efficiency. We provide relevant information about individual components of the hydrological cycle and quantify short‐term hydrological variability. For validation, we compare the modeled total water storages (TWS) with GRACE (Gravity Recovery and Climate Experiment) data with a very good agreement where GRACE uncertainties are low. The approach exemplifies the potential of GRACE for validating even regional scale hydrological applications in remote and hard to access mountain regions. We use modeled time series of individual hydrological components to characterize the effect of climate variability on the hydrological cycle. We demonstrate that glaciers play a twofold role by providing roughly 35% of the annual runoff of the Panj River basin and by effectively buffering runoff both during very wet and very dry years. The modeled glacier mass balance (GMB) of −0.52 m w.e. yr−1 (2002–2013) for the entire catchment suggests significant reduction of most Pamiri glaciers by the end of this century. The loss of glaciers and their buffer functionality in wet and dry years could not only result in reduced water availability and increase the regional instability, but also increase flood and drought hazards.
Plain Language Summary
Glaciers store large amounts of water in the form of ice. They grow and shrink dominantly in response to climatic conditions. In Central Asia, where rivers originate in the high mountains, glaciers are an important source for sustainable water availability. Thus, understanding the link between climate, hydrology, and glacier evolution is fundamental. Some instruments mounted on satellites are capable of monitoring glaciers. However, the potential of these sensors is limited by technical constraints that will affect the availability and precision of the products. In order to overcome these shortcomings and investigate glacier dynamics, we use a numerical model that represents the relevant processes of the hydrological cycle with a very fine spatial and temporal resolution. We validate model results with snow cover observations and measurements of the total amount of water stored in the region. We demonstrate that this approach is valid and could facilitate studies in other cold climate regions. Our results show that glaciers buffer extreme weather conditions to provide sustainable river flow. This functionality is put in jeopardy due to the currently observed glacier retreat, in the Pamir Mountains.
Key Points
Upscaling of regional hydrological model to the greater Pamir area using multisource validation data
Glaciers buffer extreme meteorological events and provide sustainable river runoff
Regional climatic differences substantially affect the hydrological cycle and its evolution
Surface processes involve complex feedback effects between tectonic and climatic influences in the high mountains of Pamir. The ongoing India–Asia collision provokes the development of ...east–west-trending mountain ranges that impose structural control on flow directions of the Pamir rivers. The evolving relief is further controlled by strong moisture gradients. The decreasing precipitations from the southern and western margins of the Pamir Plateau to its center, in their turn, control the emplacement of glaciers. Chronologies of glacial records from the Pamir Plateau attest for strong climatic variability during the Quaternary. Corresponding remnants of glacial advances suggest glacial morphodynamic restricted to >4,000 m a.s.l. since marine isotope stage 4. The Panj, the trunk river of Pamir, deflects from the predominant westward drainage, connecting its main tributaries at the western margin of the drainage basin. The geometry of the river network and the pattern of incision characterize the Panj as a composite river. River reaches of indicated low incision coincide with west-trending valleys, parallel to domes and their bounding faults. Valley shape ratios reflect increased incision in north-trending sections, but do not match with changes in the catchment geometry or erodibility of rock types. Modelled riverbed profiles distinguish three Panj reaches. The upstream increase in convexity suggests successive river captures in response to local base-level changes. The northward-deflected river reaches link the local base levels, which coincide with the southern boundaries of the Shakhdara and Yazgulom Dome and Darvaz Range. We argue that tectonics plays a large role controlling the drainage system of the Panj and hence surface processes in the Pamir mountains.
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