M Einali; S Alirezaei; R Bakker
Abstract
The Baghkhoshk porphyry copper system is located in the southern part of the Cenozoic Urumieh-Dokhtar magmatic belt of Iran. Mineralization in Baghkhoshk is associated with two shallow diorite-monzodiorite and granodiorite bodies that intruded the older andesitic volcanic rocks. Both intrusions are extensively ...
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The Baghkhoshk porphyry copper system is located in the southern part of the Cenozoic Urumieh-Dokhtar magmatic belt of Iran. Mineralization in Baghkhoshk is associated with two shallow diorite-monzodiorite and granodiorite bodies that intruded the older andesitic volcanic rocks. Both intrusions are extensively altered by hydrothermal fluids into potassic, phyllic, and propylitic assemblages. Mineralization occurs as quartz-sulfide stockworks as well as sulfide disseminations in both intrusions and to a lesser extent in the host volcanic rocks. Two types of quartz veinlets can be distinguished in the Baghkhoshk porphyry system: 1) quartz+ chalcopyrite+ pyrite± molybdenite veinlets (mineralized veinlets); and 2) quartz± pyrite veinlets (barren veinlets). The intrusions display distinct enrichments in large-ion lithophile elements and rare earth elements relative to high-field strength elements and heavy rare earth elements, and distinct Nb, Ta and Ti troughs that are characteristic of subduction-related magmatic arcs. On various diagrams separating tectonic settings, the intrusions plot in the continental arc domain. Three main types of fluid inclusions were identified in quartz from mineralized veinlets: low salinity (4-8 mass% NaCl equivalent), vapor-rich inclusions; high salinity (mainly in the range of 32.5-35 mass% NaCl equivalent), poly-phase inclusions; and low to moderate salinity (mainly in the range of 4-10 mass% NaCl equivalent), liquid-rich inclusions. The vapor-rich inclusions yielded homogenization temperatures ranging between 325 and 434 °C, with a mode at 380-420 °C. Laser Raman microspectroscopic analysis confirmed the presence of CO2 gas and chalcopyrite daughter crystals in the vapor-rich inclusions. The high salinity, poly-phase inclusions were homogenized to liquid at temperatures of mainly 300-375 °C. The liquid-rich inclusions were homogenized at temperatures between 150 and 384 °C, with most of the measurements falling in the range of 200-250 °C and 300-375 °C. The salinities and homogenizaion temparatures for fluid inclusions in quartz from the barren veinlets were found to be 0.5-4 mass% NaCl equivalent and 200-240 °C, respectively. The fluid inclusion data suggest that Cu was originally accommodated into the system by a hot (380-420°C), low salinity (4-8 mass% NaCl equivalent), CO2-bearing, vapor-rich or supercritical fluid. A considerable drop in temperature at constant salinity from vapor-rich to liquid-rich inclusions in the mineralized veinlets suggests that cooling was the main control on ore formation as stockworks and sulfide disseminations. In the later stages of the hydrothermal activity, low salinity, Cu-poor fluids gave rise to abundant barren veinlets consisting essentially of quartz and pyrite.
L Salehi; I Rasa; S Alirezaei; A Kazemi Mehrnia
Abstract
The Madan Bozorg deposit is located in the Abbas Abad mining district, about 130 km east of Shahroud. The area is covered by a NE-SW trending belt of intermediate-mafic lava flows and pyroclastic materials, as well as interlayered sedimentary rocks. Eight copper deposits have been identified in the district. ...
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The Madan Bozorg deposit is located in the Abbas Abad mining district, about 130 km east of Shahroud. The area is covered by a NE-SW trending belt of intermediate-mafic lava flows and pyroclastic materials, as well as interlayered sedimentary rocks. Eight copper deposits have been identified in the district. Based on the chemistry, the volcanic rocks can be classified as trachyandesite, trachyandesitic basalt and trachybasalt; the rocks display high potassium calc-alkaline to shoshonitic affinities and bear geochemical attributes characteristic of continental arc settings. The Madan Bozorg deposit is hosted in trachyandesite with porphyritic to megaporphyritic, glomeroporphyritic and amygdaloidal textures. Based on field observations, microscopic studies, Raman spectroscopy and XRD results, two types of alteration, regional and local, can be distinguished. The regional or background alteration, is comparable to a propylitic assemblage and occurs in mineralized and non- mineralized volcanic units. Local alteration associated with copper mineralization includes calcic, silicic, sericitic, chloritic, zeolitic and hematitic. Copper mineralization occurs as disseminated, vein- veinlet, replacement, stockworks and irregular open space fillings. Based on microscopic studies and EPMA data, chalcocite group minerals (chalcocite, djurleite, anilite, digenite and covellite) are the main ore minerals and are accompanied by subordinate bornite, pyrite and hematite. Secondary minerals include covellite, malachite, azurite, chrysocolla and goethite. Nonmetallic minerals are quartz, chlorite, epidote, calcite, and chalcedony. Based on fluid inclusion studies on coexisting quartz, homogenization temperatures are between 90 to 268°C with an average of 176° C. Salinities vary between 3.38 to 21.96 (average, 13.21) wt% NaCl eq. Fluid density varies between 0.8 to 1.1 g.cm-3. The depth of fluid inclusion trapping is estimated to be less than 200 meters, and ore formation occurred at pressures less than 50 bars. The host rocks, ore mineralogy, ore textures and structures, and fluid inclusions characteristics in Madan Bozorg deposit are similar to those reported from Manto type copper deposits in Mesozoic-Cenozoic volcanic belts in South America and elsewhere.
M Alimohammadi; S Alirezaei; M Ghaderi; D.J Kontak
Abstract
The Daraloo and Sarmeshk copper deposits lie in a northwest-trending fault zone, 10 km long and 0.5-1 km wide in the southern section of the Kerman copper belt, south Iran. The area is marked by a series of Late Eocene-Oligocene granodiorite and Miocene porphyritic tonalite-granodiorite intrusions that ...
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The Daraloo and Sarmeshk copper deposits lie in a northwest-trending fault zone, 10 km long and 0.5-1 km wide in the southern section of the Kerman copper belt, south Iran. The area is marked by a series of Late Eocene-Oligocene granodiorite and Miocene porphyritic tonalite-granodiorite intrusions that cut Eocene andesitic and basaltic lava flows and pyroclastic rocks. Mineralization in both deposits is associated with the Miocene porphyritic intrusions. Both volcanic and plutonic rocks are intruded by post-mineralization diabasic, andesitic and rhyolitic dykes. Representative samples from various rocks were analyzed for major oxides and a wide range of elements. The samples display calc-alkaline affinities; the volcanic rocks are metaluminous, and the intrusive rocks are peraluminous. On primitive mantle- and chondrite-normalized plots, all rocks are characterized by enrichment in large ion lithophile elements and light rare earth elements, relative to high field strength elements and heavy rare earth elements. The features, combined with the negative anomalies for Nb, Ta, and Ti, are characteristic of the subduction- related magmas.The Miocene tonalites are most fractionated, with LaN/YbN ratios ranging between 7.81 and 18.21. This ratio in granitoid rocks is between 6.61 and 7.56. The volcanic rocks are least fractionated, with LaN/YbN ratios from 1.52 to 5.16 .The geochemical attributes of the intrusive bodies from both Daraloo and Sarmeshk are consistent with significant contribution from sediments and crustal materials in the source area, compared to that introduced by fluids released from a subducting slab. The volcanic rocks are, however, appear to have been least affected by crustal materials, but slightly influenced by slab-derived fluids. Plots of samples from all plutonic and volcanic rocks on various discrimination diagrams indicate a transition from an island-arc setting in Paleocene-Eocene to a continental margin volcanic arc setting in Neogene. This is in agreement with earlier works on the evolution of the Kerman belt.
