Exploration Of Porphyry Copper Deposits Research Articles

Low temperature thermochronology reveals tilting of crystalline bodies, Halilaga porphyry Cu-Au deposit, NW Anatolia: Implications for exploration of porphyry copper deposits and interpretation of low-temperature thermochronology data for regional tectonics

Because most crystalline bodies lack intrinsic paleo-horizontal information, their tilting cannot be measured directly. Their vertical movement, however, may be tracked by low-T thermochronology (LTT) tools. Because tilting is caused by differential vertical movements, it can be understood if the rate of differential movements is determined. In this regard, here we apply a new LTT-based approach to calculate the orientation of a tilted crystalline body, the Halilaga Cu-Au deposit, in NW Anatolia. Orientation is consistent with the one calculated from a drillhole-based 3D model of the deposit. This reveals the significance of tilting calculations for the exploration of porphyry Cu deposits. On the other hand, and more importantly, it emphasizes the importance of tilting calculations for geological applications such as LTT-based exhumation histories of samples taken from vertical profiles, and paleomagnetic studies. AHe data from the Halilaga deposit reveals the earliest response to the Aegean back-arc extension at ∼ 24 Ma in the north of Western Anatolia. Lastly, thermal models, the new complementary datasets for the tectonic evolution of the region, show that the Halilaga deposit was exhumed to the surface by the coupling effects of Aegean extension and westward propagation of the North Anatolian Fault, which occurred not earlier than 2 Ma.

Geochronology and geochemistry of porphyritic intrusions in the Duolong porphyry and epithermal Cu-Au district, central Tibet: Implications for the genesis and exploration of porphyry copper deposits

The Duolong district in central Tibet hosts a number of porphyry as well as high sulfidation epithermal copper–gold deposits and prospects, associated with voluminous calc-alkaline volcanism and plutonism. In this study, we present new geochronological, geochemical, isotopic and mineralogical data for both economically mineralized and barren porphyritic intrusions from the Duobuza and Naruo porphyry Cu–Au deposits. Zircon U–Pb analyses suggest the emplacement of economically mineralized granodiorite porphyry and barren granodiorite porphyry at Naruo deposit took place at 119.8±1.4Ma and 117.2±0.5Ma, respectively. Four molybdenite samples from the Naruo deposit yield an isochron Re–Os age of 119.5±3.2Ma, indicating mineralization occurred synchronously with the emplacement of the early granodiorite porphyry. At Duobuza deposit, the barren quartz diorite porphyry intruded at 119.5±0.7Ma, and two economically mineralized intrusions intruded at 118.5±1.2Ma (granodiorite porphyry) and 117.5±1.2Ma (quartz diorite porphyry), respectively. Petrographic investigations and geochemical data indicate that all of the porphyritic intrusions were oxidized, water rich, and subduction-related calc-alkaline magmas. Zircons from the porphyritic intrusions have a wide range in the εHf (0–11.1) indicating that they were sourced from mixing of mantle-derived mafic, and crust-derived felsic melts. Moreover, the variation of trace element content of plagioclase phenocrysts indicates that the magma chambers were recharged by mafic magmas.Comparison of the composition of amphibole phenocrysts indicates the porphyry copper–gold mineralization at Duolong was generated in magma chambers at low crystallization temperatures and pressures (754° to 791°C, 59M to 73MPa, n=8), and under highly oxidizing conditions (ΔNNO 2.2 to 2.7, n=8). In contrast, barren intrusions were sourced from the magma chambers with higher crystallization temperatures and pressures (816° to 892°C, 111 to 232MPa, n=22) that were less oxidizing (ΔNNO 0.6 to 1.6, n=22). The requirement for a thermal contrast is supported by the declining of Ti content in magnetite crystals in barren intrusions (12,550 to 34,200ppm) versus those from economically mineralized intrusions (600 to 3400ppm). Moreover, the V content in magnetite crystals from economically mineralized intrusions (990 to 2510ppm) is lower than those recorded from barren intrusions (2610 to 3510ppm), which might reflect the variation in oxidation state of the magma. The calculated water solubility of the magma forming the economically mineralized intrusions (3.2–3.7wt%) is lower than that of magma forming the barren intrusions (4.6–6.4wt%). Based on the chemical–physical characteristics of economically mineralized magma, our study suggests that the development of porphyry Cu–Au mineralization at Duolong was initiated by shallow-level emplacement of a magma that crystallized at lower temperatures and pressures. Experimental studies show that copper and water solubilities in silicate melts decrease with falling temperatures and pressures, indicating metals and ore-forming fluids are more likely to be released from a magma reservoir emplaced at shallow crustal levels. We propose the magnetite might be a convenient exploration tool in the search for porphyry copper mineralization because the variations in Ti and V content of mineral concentrates and rock samples are indicative of barren versus mineralized intrusions.

Application of ASTER data for exploration of porphyry copper deposits: A case study of Daraloo–Sarmeshk area, southern part of the Kerman copper belt, Iran

The Cenozoic Urumieh–Dokhtar Magmatic Belt (UDMB) of Iran is a major host to porphyry Cu±Mo±Au deposits (PCDs). Most known PCDs in the UDMB occur in the southern section of the belt, also known as the Kerman Copper Belt (KCB). Three major clusters of PCDs are distinguished in the KCB and include the Miduk, Sarcheshmeh and Daraloo clusters. The Daraloo and Sarmeshk deposits occur in a northwest–southeast-trending fault zone that is characterized by the presence of a narrow zone of alteration–mineralization that contains a series of Oligocene granitoids and Miocene porphyritic tonalite–granodiorite plutons that cut Eocene andesitic lava flows and pyroclastic rocks. Here we use various techniques, including different ratio images, minimum noise fraction, pixel purity index, and matched filter processing to process ASTER data (14 bands) and generate maps that portray the distribution of hydrothermal minerals (e.g., sericite, kaolinite, chlorite, epidote and carbonate) related to PCD alteration zones. In order to validate the ASTER data, follow-up ground proofing and related mineralogical work was done which, in all cases, proved to be positive. The results of this work have identified the regional distribution of hypogene alteration zones (i.e., phyllic, argillic, propylitic and silicic), in addition to areas of secondary Fe-oxide formation, which are coincident with known sites of PCDs. The regional distribution and extent of the alteration zones identified also highlighted the role of regional structures in focusing the mineralizing/altering fluids. These results demonstrate very convincingly that ASTER imagery that uses the appropriate techniques is reliable and robust in mapping out the extent of hydrothermal alteration and lithological units, and can be used for targeting hydrothermal ore deposits, particularly porphyry copper deposits where the alteration footprint is sizeable.

Rule of Structural Factors in Formation of Porphyry Copper Deposits in South Western Part of Kerman Area, Iran

Kerman area is located in southern parts of central Iranian volcanic belt. The area under study is located in the southern part of this complex copper mineralization in the area, which is mainly porphyry type and is associated with extensive hydrothermal alteration. This area has a great potential as far as tertiary porphyry copper deposits are concerned. To the exploration of porphyry copper deposits in study area, we have analyzed the lineaments. The lineaments interpreted out from ETM + (band8) data is recognized as another method for locating porphyry type copper mineralization. There is a close correlation between photo lineament factor values and the known copper mineralization in the area. The relationship between 16 porphyry copper deposits with faults and fractures in the area is studied. Photo lineament factor assessments by using satellite photos indicate a strong relationship between a number of lineation intersection in each cell refer to an amount of average lineation in whole map (c/C ratio). In the study area, ratio of c/C even has more relationship refers to PF factor that has previously described in the papers.

Geochronologic constraints on magmatic intrusions and mineralization of the Zhunuo porphyry copper deposit in Gangdese, Tibet

In situ zircon U-Pb ages for the recently discovered Zhunuo porphyry copper deposit in the western part of the Gangdese metallogenic belt in Tibet were determined by sensitive high-resolution ion microprobe (SHRIMP). The ages can be divided into two separate groups, reflecting more than four major tectono-magmatic events in the area. The 62.5±2.5 Ma age of inherited zircons may be related to the volcanic eruption of the Linzizong Group formed shortly after the India-Asia continental collision. The 50.1±3.6 Ma age most likely corresponds to the time of underplating of mantle-derived mafic magma in Gangdese. The 15.6±0.6 Ma age obtained from magmatic zircons is interpreted as the age of crystallization of the Zhunuo ore-forming porphyry. Finally, a molybdenite Re-Os isochron age of 13.72±0.62 Ma is consistent with another zircon U-Pb age of 13.3±0.2 Ma, representing the time of copper mineralization. These ages, in combination with available literature data, indicate that magmatic crystallization and copper mineralization in the Gangdese metallogenic belt became gradually younger westward, and further suggest that the Zhunuo porphyry copper deposit was formed in the same tectonic stage as other porphyry copper deposits in the eastern and central Gangdese belt. This conclusion provides critical information for future exploration of porphyry copper deposits in western Gangdese.

Synergetic use of remote sensing and geophysical data for exploration of porphyry copper deposits, using GIS

Darrehzar porphyry copper deposit is situated in the Urumieh-Dokhtar magmatic assemblage of central Iran. In this paper, the integration of multiple geodata sets has been carried out using geographic information system for mapping lithology or hydrothermally altered rocks and also in selecting the best discriminating data elements for exploration of porphyry copper deposits located in areas with similar geological setting and climatic conditions. Principal component analysis is found useful for reducing large data sets into a few principal components. The integration of various geophysical data with SPOT image data through GIS has shown that the hydrothermal alteration and lithology can be mapped with more efficiency.

Multi-metal soil geochemistry: A tool for identification and exploration of porphyry copper deposits: Two examples from Peru

Abstract Two porphyry copper-type mineral occurrences were prospected using multi-element soil geochemistry with the purpose of their selection, identification and evaluation and in order to outline a drill target. The two occurrences are located in very different climatic zones: one in the north of Peru at an altitude of 2500 m, in moderate but humid climatic conditions; the other in a warm desert area at an altitude of 1500–1800 m. For each soil sample, Cu, Mo, Pb, Zn, Au, Mn, Fe, and K were determined. In both cases, the values were not significantly influenced by weathering processes except for Cu, which showed high mobility in desert conditions. A system of concentric zoning with Cu, Mo, Au, and K in the center and Pb, Zn, Mn, and Fe forming the outer zone, together with field observations enabled us: (1) to confirm the existence of a zoned hydrothermal system, indicating porphyry copper-type mineralization; (2) to outline a target area for drilling more easily than by using only soil Cu values, which are often unreliable due to the high mobility of the metal; and (3) to follow the migration of elements like Mn, Zn, Fe, and Pb as a result of hydrothermal alteration.

Geology and exploration of porphyry copper deposits in North Sulawesi, Indonesia

Newly discovered porphyry copper deposits in North Sulawesi (Celebes) are located in two principal districts, each with several centers of porphyry copper mineralization. The deposits were discovered by reconnaissance stream silt geochemistry, which detected anomalies of the order of 500 to 1,000 ppm Cu, against a background of 100 ppm Cu, with anomalous trains extending up to 3 km downstream. Subsequent follow-up revealed stream silt anomalies as high as 1.5 percent Cu. Ore targets were developed by detailed stream silt and rock geochemistry together with geologic mapping of lithology, alteration, sulfide distribution, and quartz veining. Gold proved superior to copper, lead, zinc, and molybdenum in the identification of centers of strongest hypogene mineralization, especially in the case of leached cappings, where a strong gold anomaly accompanied by a weak copper anomaly indicates high potential for supergene-enriched ore at depth.In the economically more important district (Tombuililato) high-level quartz diorite porphyry stocks intrude a middle to upper Tertiary island-arc sequence, consisting principally of andesite and rhyolite. Supergene-enriched mineralization is developed in some of the stocks, which are characterized by intense alteration and generally moderate sulfide contents (3-5 volume percent). Ore-grade hypogene mineralization is restricted to the porphyry and to a narrow andesitic wall-rock contact zone. These copper centers occur within a broad zone (5X15 km) of pyritic mineralization, which is best developed in the Tertiary rhyolitic rocks. In the other district (Tapadaa), copper mineralization occurs in complex dioritic plutons whose sulfide contents, copper grades, and degree of enrichment are generally lower than at Tombuililato.Hydrothermal alteration is characterized by the widespread occurrence of strong advanced argillic alteration and the presence of albite or montmorillonite, rather than potash feldspar, in the ore zone. Advanced argillic mineral assemblages comprise various combinations of quartz, andalusite, corundum, diaspore, pyrophyllite, alunite, kaolinite, and specularite. The highest copper grades are generally accompanied by sericite-albite or sericite-montmorillonite alteration, but biotite, chlorite, magnetite, and some advanced argillic minerals are present at least locally in the ore zone. Copper centers in the Tombuililato district occur within a broad zone of advanced argillic-altered rock which approximately coincides with the pyritic sulfide system. Drilling has shown that ore-grade mineralization underlies some areas of advanced argillic alteration at less than 100 m depth. In some cases this represents a change from advanced argillic to clay-sericite alteration with depth, but ore-grade hypogene copper mineralization does occur with advanced argillic alteration of quartz-diaspore-pyrophyllite type. In this case the total sulfide content is commonly high (3-10 volume percent) and the sulfide assemblage is characteristically pyrite-bornite-chalcopyrite.Exceptional abundance of advanced argillic alteration in North Sulawesi is thought to relate to the presence of albite or montmorillonite instead of potash feldspar, to the dioritic nature of the host rocks, and to unusually acidic ore fluids. Mineralogical data suggest that copper mineralization and alteration in the Tombuililato district may have occurred at relatively low temperatures (350 degrees -400 degrees C). The Tapadaa deposits are thought to be root zones of high-level stocks whose eroded parts were like the deposits now exposed at Tombuililato.