Halogen signatures of biotites from the Maher-Abad porphyry copper deposit, Iran: characterization of volatiles in syn- to post-magmatic hydrothermal fluids (original) (raw)
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Mineralogy and Petrology, 2008
The Dalli porphyry copper deposit is hosted by the Miocene-Pliocene subvolcanic plutons with chemical composition from diorite to granodiorite that intruded into the andesitic and dacitic volcanic rocks and variety of sedimentary sequences within the Urumieh-Dokhtar Magmatic Arc. Three main hydrothermal alteration zones including potassic, phyllic and propylitic types have been described in the volcano-plutonic rocks. Early hydrothermal alteration started with potassic style in the central part of system produced a secondary biotite-K-feldspar-magnetite assemblage and accompanies to chalcopyrite and pyrite mineralization. This paper summarizes the detailed biotite mineral chemistry from the potassic and phyllic alteration zones. The FeO, TiO 2 , MnO, K 2 O, and Na 2 O (wt.%) concentrations of biotite from the phyllic alteration zone are lower than biotite from the potassic alteration zone. The F and Cl (wt.%) contents of biotite from the potassic alteration zone display relatively high positive correlation with the X Mg. The fluorine intercept values [IV (F)] from the potassic and phyllic alteration zones are strongly positively correlated with the fluorine/chlorine intercept values [IV (F/Cl)]. Biotite geothermometry for the potassic and phyllic alteration zones yield a range from 402°to 450°C and 280°to 343°C, respectively at Dalli porphyry copper deposit. The scatter in log (X F /X OH) ratios vs. X Mg and X Fe plots also reflects the evidence of biotite formed under dissimilar composition and temperature conditions in the potassic and phyllic alteration zones. Calculated log fugacity ratios of (fH 2 O/fHF), (fH 2 O/fHCl), and (fHF/ fHCl) show that hydrothermal fluids associated with the potassic alteration were distinctively different from fluids those associated with the phyllic alteration zone at Dalli porphyry copper deposit. The relation between log (fH 2 O/ fHCl) and log (fH 2 O/fHF) fugacity ratios indicates that biotite from the Dalli volcano-plutonic rocks is distinctly similar to biotite from the porphyry copper deposit at Bingham.
Journal of Geochemical Exploration, 2009
Miduk hypogene and supergene porphyry Cu-Mo mineralization occurs within the Miocene porphyritic quartz-diorite and host Eocene plagioclase-hornblende phyric andesitic pyroclastic and flow sequence. Both the host rocks were extensively altered by hydrothermal fluids to dominantly potassic, phyllic, and argillic with interstitial to distal propylitic types. Biotite-bearing assemblages from the proximal potassic zone are dark to light brown and have X phl from 0.56 to 0.68; F contents range from 0.15 to 1.8 wt.% and Cl contents range from 0.19 to 0.28 wt.%. Fluorine contents in the biotite negatively correlate with X phl and X Ti and Cl contents, and positively correlate with X phl and SiO 2 . Calculated log (fH 2 O/fHF), log (fH 2 O/fHCl), and log (fHF/fHCl) values of fluid in equilibrium with these biotites ranging from 5.5 to 6.40, 4.64 to 4.79, and − 2.54 to − 1.68, respectively. Established halogen fugacity ratio contour lines are transected by the steeper slope of measured values of biotite composition; this suggests the fluid composition, fO 2 and fS 2 of the fluids, and reaction between wall rock and hydrothermal fluids play a key role in the resultant halogen fugacities recorded in biotite that is critical to interpreting metal complexing behaviour during magmatic-hydrothermal evolution. The intercept values of F [IV(F)] and Cl [IV(Cl)] for biotite from the potassic zone are similar to those of related plutonic rocks and other porphyry Cu deposits; the IV(Cl) tend to be more Cl-rich than comparable values of common igneous rocks. F-rich to Fpoor biotite crystals from the Miduk deposit show a narrow range of F/Cl intercept values [IV(F/Cl)] consistent with porphyry Cu ore-forming fluids. ). The timing of fluid-vapour saturation affects the partitioning of F and Cl between granitic magmas, minerals, and magmatic hydrothermal fluids, which strongly controls metal complexing, and mass transport to the site of hydrothermal ore deposition . The temperature, salinity, and pH of F-and Cl-bearing fluids are also responsible for the alteration associated with porphyry emplacement
Ore Geology Reviews
The Sungun Porphyry copper-molybdenum deposit, in the northwestern part of the post-collisional Urumieh-Dokhtar magmatic arc, developed as a consequence of hydrothermal alteration related to the emplacement of the Sungun quartz monzonite porphyry stock into Eocene volcanic rocks. Based upon petrographic characteristics, back-scattered electron images, and compositional attributes, biotite from the Sungun Porphyry copper-molybdenum deposit was grouped into least-altered magmatic biotite (LA-Mbt), least-altered equilibrated magmatic biotite (LA-Eq Mbt), equilibrated magmatic biotite (Eq-Mbt), and secondary hydrothermal biotite (S-Hbt) types. The LA-Mbt from the mineralized zone have high TiO 2 (3.92-4.33 wt%) compared to LA-Eq Mbt (3.81-4.20 wt %), Eq-Mbt (2.75-3.85 wt%), and S-Hbt (0.27-3.00 wt%). The LA-Mbt of the barren dike is also characterized by high TiO 2 (4.17 wt% on average). Na 2 O, SiO 2 , and MnO (wt%) of biotite are systematically different between mineralized intrusions and barren ones. The highest amounts of Na 2 O (0.39-0.58 wt%) and MnO (0.11-0.18 wt %) are found in the LA-Mbt of the barren dike, which contrast with LA-Mbt of the mineralized zone having 0.08-0.15 wt% Na 2 O and 0.03-0.14 wt% MnO. Low SiO 2 values (36 wt% on average) are characteristic of LA-Mbt from the barren dike in comparison with LA-Mbt of the mineralized zone (37 wt% on average). The SO 3 contents in LA-Mbt of the mineralized zone (0.03-0.12 wt%) are much higher than those for LA-Mbt of the barren dike (0.01-0.04 wt%). The fluctuations in SO 3 content of S-Hbt reflect a complex history of formation of S-Hbt in two stages. One group of S-Hbt has SO 3 > 0.04 wt% and are principally related to the potassic (medium-high)/phyllic (low) assemblage, forming with magnetite at high oxygen fugacity, whereas the second group has SO 3 < 0.04 wt% and is related to the phyllic (high)/argillic (low) assemblage, having formed during a stage of sulfide mineralization. The calculated oxygen fugacities (ƒO 2) of 10 −15.4-10 −13.8 for the mineralized zone of the Sungun Porphyry Cu-Mo deposit lie completely within the domain of logƒO 2 > ΔFMQ+2 (where FMQ is the fayalite-magnetite-quartz oxygen buffer), typical of oxygen fugacities associated with Cu-Mo porphyry mineralization. Altered biotite types have higher Cl contents than the least altered varieties, indicating that Cl may be used as an indicator of post-magmatic hydrothermal processes. The range of F contents (0.336-0.621 wt%) for the LA-Mbt of the mineralized zone is higher than those of the LA-Mbt types of the barren dike (0.219-0.347 wt%). Fluorine in biotite may be used as an exploration vector to characterize mineralized versus subeconomic porphyry Cu-Mo systems. 1975; Parry and Jacobs, 1975); and (iii) investigating the physicochemical features of ore fluids, as well as their evolution through the entire mineralization process (Munoz, 1984; Lentz, 1992, 1994; Selby and Nesbitt, 2000). Several previous studies of biotite chemical compositions from porphyry Cu systems focused on the calculation of F and Cl contents, with the objective of identifying mineralized and barren plutons (e.g.,
Journal of Geochemical Exploration
The geochemical characteristics of four biotite types comprising least-altered magmatic biotite (LA-Mbt), leastaltered equilibrated magmatic biotite (LA-Eq Mbt), equilibrated magmatic biotite (Eq-Mbt), and secondary hydrothermal biotite (S-Hbt) types from a subeconomic low-grade porphyry Cu system named Sonajil are compared with the economic high-grade Sungun porphyry Cu-Mo deposit situated in the Western Alborz-Azerbaijan structural zone of Iran; the proximity of the two porphyry copper deposits helps to evaluate mineralization potential of the intrusive bodies. The classification scheme for biotite types is based on petrographic data, back-scattered electron images, and compositional attributes. Whereas both of the S-Hbt types at Sonajil and Sungun are related to the overlapping alteration zones of high potassic / low phyllic, the S-Hbt types at Sungun are Mg-rich and fall within the compositional field confined by two endmembers of eastonite and phlogopite. The S-Hbt types at Sonajil are Fe-rich plotting in the compositional field enclosed by two endmembers of eastonite and siderophyllite. The mean of MgO, MnO, TiO 2 , Na 2 O, SiO 2 , and F (wt%) contents of the biotites help in characterizing the geochemical features of the mineralized magmatic rocks contrasted with subeconomic intrusions. Biotite types of the Sungun Porphyry stock display much higher SO 3 contents (0.06 wt% on average) compared to those of biotite types of the Sonajil Porphyry stock (< 0.01 wt% on average). Fluorine contents (0.9 wt% F on average) in the Sungun Porphyry biotites are the highest ones, whereas the biotite types of the Sonajil Porphyry stock have 0.8 wt% F (on average). Biotite types of the Sonajil and Sungun Porphyry stocks exhibit approximately equal Cl contents (0.15 wt% on average). Magmatic biotites of the productive Sungun Porphyry stock were characterized by higher temperatures (760°C on average) compared to those of unproductive Sonajil Porphyry stock (747°C on average). The LA-Mbt types of the Sonajil Porphyry point to oxygen fugacities (ƒO 2) with values ranging from 10 −16.27 to 10 −14.40 bars, while LA-Mbt types at Sungun deposit were formed under oxygen fugacities between 10 −15.4 to 10 −13.8 bars. There is a positive correlation between the amount of Cu (wt%) in the Porphyry stocks and the wt% SO 3 in the biotites of Porphyry stocks. The hydrothermal fluids related to alteration zones in the subeconomic Sonajil have approximately the same range of log(ƒH 2 O)/(ƒHCl) and log(ƒHF)/(ƒHCl) values to those of fluids associated with other economic deposits, such as Los Pelambres and Casino. Therefore, it can be recommended that evaluating of log(ƒH 2 O)/(ƒHCl) and log(ƒHF)/ (ƒHCl) ratios of fluids in equilibrium with biotites alone cannot be a discriminating parameter. Confirmation by SO 3 (wt%) content of the biotite types, by linkage between SO 3 content of biotites and Cu grade, by halogen (wt % F and Cl) chemistry of biotite types, by halogen intercept values of F, Cl, and F/Cl, and by hydrothermal fluid halogen fugacity ratios, all illustrate the capacity of SO 3 content (wt%) of biotites to be a reliably exploration index and highlight the critical role of fluorine compared to chlorine in discrimination of unproductive and productive porphyry Cu systems.
Ore Geology Reviews, 2010
The giant Sarcheshmeh porphyry Copper deposit is located 65 km southwest of Kerman City, southeastern Iran. Numerous Miocene porphyry stocks and dykes intruded thick sequences of Upper Cretaceous sedimentary and Eocene volcanic rocks. Hypogene and supergene porphyry Cu mineralization occurs within the granodioritic porphyry and host rock sequence, which was extensively altered to a dominantly potassic, phyllic, and argillic assemblage with interstitial to distal propylitic types. Biotite-bearing assemblages occur as both primary phenocrysts and secondary replacements showing variable size, colour, and shape. Fluorine contents (0.22 to 1.33 wt.%) and X Mg (0.54 to 0.71) in biotites from the potassic and phyllic zones are higher than those of non-mineralized granitoids (F = 0.09 to 0.56 wt.%, X Mg = 0.43 to 0.54), whereas their Cl contents (Cl = 0.05 to 0.24 wt.%) are lower than those of the nonmineralized granitoids (Cl = .0.11 to 0.45). The biotites from the phyllic zone have higher log (fH 2 O/fHF) and log (fH 2 O/fHCl) values than those of the potassic zone, as well as the granitoid and andesitic dykes. The log (fHF/fHCl) values determined for the granitoid, potassic and phyllic zones are similar, though more negative than those of the andesitic dykes. The log (fHF/fHCl) values have a similar range for biotite from the granitoid, and potassic and phyllic zones. The halogen fugacity ratios established for fluids associated with the Sarcheshmeh deposit from their F and Cl contents in biotite show that the granitoid, potassic zone and phyllic zone are increasingly affected by meteoric waters. The fluids that circulated in the phyllic zone are predominantly of meteoric origin, possibly overprinting original phyllic zone halogen contents. The Cl intercept values of biotite in the granitoid, and phyllic and potassic are similar to other ore-forming systems and tend to be more Cl-rich than Cl-intercept values of biotites in common igneous rocks. Calculated F/Cl intercept values for biotite in the granitoid and potassic zone are also consistent with many other porphyry copper forming systems.
Ore Geology Reviews, 2015
The study presents textural and mineral chemistry data, as well as whole-rock and mineral separate Os-isotopic compositions for PGM assemblages from deep portions of the oceanic mantle. The extensive data set of Os-isotope compositions of intimately intergrown grains of Os-rich alloy and Ru-Os sulfide from ophiolite-type massifs of different ages is firstly evaluated. The Os-isotope results identify a restricted range of 'unradiogenic' 187 Os/ 188 Os values for coexisting laurite and Os-rich alloy pairs that form 'primary' PGM assemblages at Hochgrössen, Shetland, Os/ 188 Os values have been identified in the chromitite and mineral separates from 'primary' and 'secondary' PGM assemblages, implying that the whole-rock Os-isotope budget is largely controlled by the laurite-alloy pair.
Ore Geology Reviews, 2013
The Kahang porphyry Cu deposit, located northeast of Isfahan city in central of Iran, is associated with a composite Miocene stock and ranges in composition from diorite through granodiorite to quartz-monzonite. Field observations and petrographic studies show that the emplacement of the Kahang stock occurred in several pulses, each associated with its related hydrothermal activity. Early hydrothermal alteration started with a potassic style in the central part of the system and produced a secondary biotite-K-feldspar-magnetite assemblage accompanied by chalcopyrite and pyrite mineralization. Propylitic alteration that took place at the same time as the potassic alteration occurred in the peripheral portions of the stock. Subsequent phyllic alteration overprinted earlier potassic and propylitic alterations. Biotite grains from the potassic and phyllic zones show distinct chemical compositions. The FeO, TiO 2 , MnO, K 2 O, and Na 2 O concentrations in biotite from the phyllic alteration zone are lower than those from the potassic alteration zone. The F and Cl contents of biotite from the potassic alteration zone display relatively high positive correlation with the X Mg. The fluorine intercept values [IV(F)] from the potassic and phyllic alteration zones are strongly correlated with the fluorine/chlorine intercept values [IV(F/Cl)]. Biotite geothermometry for the potassic and phyllic alteration zones, based on the biotite geothermometer of Beane (1974), yields a temperature range of 422°to 437°C (mean = 430°C) and 329°to 336°C (mean = 333°C), respectively. The position of data in log (X F /X OH) ratio vs. X Mg and X Fe diagram suggests that biotite formed under dissimilar composition and temperature conditions in the potassic and phyllic alteration zones. Calculated log fugacity ratios of (fH 2 O/fHF), (fH 2 O/ fHCl), and (fHF/fHCl) show that hydrothermal fluids associated with the potassic alteration were distinctively different from those fluids associated with the phyllic alteration zone at Kahang porphyry Cu deposit. The results of this research indicate that the chemistry of biotite is related to the chemical composition of the magma and the prevailing physical conditions during crystallization.
Igneous biotite has been analyzed from three I-type calc-alkaline intrusives of the Shah Jahan Batholith in NW Iran, which host several Cu-Mo-Au prospects. The X Mg (Mg/Mg+Fe) value of biotite is the most significant chemical factor and the relatively high value of X Mg corresponds to relatively high oxidation states of magma (estimated ƒ O2 is mostly 10 -12.5 to 10 -7.5 bars), which is in good agreement with their host intrusions' setting and related ore occurrences. Based on criteria of Al IV and Al VI values, all studied biotites are primary (Al VI = 0), and based on Al total values (2.23-2.82 apfu) are in distinctive ranges of mineralized granitoid (Al total =3.2 apfu).
Ore Geology Reviews, 2014
Copper and gold mineralization in the Maher-Abad deposit, eastern Iran, is closely related to the multiple emplacement episodes of Upper Eocene granodiorite porphyries within andesitic volcaniclastic and coeval quartz monzonite stocks. The magmatic hydrothermal fluids thereafter hydrofracturing provided appropriate conduits, formed a stockwork of quartz and quartz-sulfide veinlets within the porphyritic host rocks which were extensively altered into potassic, propylitic, phyllic, and argillic assemblages. Four main vein/veinlet groups have been identified: (A) quartz ± K-feldspar ± biotite ± anhydrite with pyrite, chalcopyrite, sporadic magnetite and pyrrhotite; (B) quartz, pyrite and minor chalcopyrite; (C) chalcopyrite, quartz and/or minor bornite, pyrite, digenite and sporadic pyrrhotite; and (D) quartz, calcite and/or clay minerals ± pyrite ± hematite ± galena. The Cu-Au mineralization is mainly associated with the early potassic (biotite) alteration zone in the deep central part of the Madanha stock. Based on the phase contents at room temperature, three types of fluid inclusions are recognized at Maher-Abad:
TURKISH JOURNAL OF EARTH SCIENCES, 2014
The Chahfiruzeh deposit is a newly discovered porphyry-style copper deposit in the southern part of the Cenozoic Urumieh-Dokhtar magmatic arc of Iran. Mineralization is associated with a Miocene quartz-diorite to quartz-monzodiorite porphyritic intrusion (Chahfiruzeh porphyry) intruded into older basaltic and andesitic lava flows and pyroclastic rocks. Alteration assemblages and alteration zoning, typical of porphyry copper deposits, are well developed. Mineralization occurs in quartz-sulfide stockworks and as sulfide disseminations in the porphyritic intrusion and the immediate wall rocks. Pyrite and chalcopyrite are the main hypogene sulfide minerals; bornite and molybdenite are rare. Representative magmatic and alteration minerals, including plagioclase, amphibole, biotite, sericite, and chlorite, are analyzed, and the data are used to constrain the crystallization conditions of the magmas and the nature and evolution of the hydrothermal fluids. The fluorine-chlorine fugacity in the magma during crystallization of the Chahfiruzeh porphyry, represented by log (fH 2 O)/(fHF)-log (fH 2 O)/(fHCl) and determined from the chemical composition of magmatic biotite, ranges between 5.23 and 6.80 and between 5.05 and 5.13, respectively. A comparison to several other intrusions associated with porphyrystyle mineralization suggests that the Chahfiruzeh intrusion crystallized at relatively high fH 2 O/fHCl ratios. The intercept value (F/ Cl) of the magmatic biotite in the Chahfiruzeh porphyry ranges from 5.5 to 7.02. The calculated F/Cl intercept values for the biotite are consistent with those reported from many other porphyry copper systems. The secondary reequilibrated biotite in the intrusion is distinguished from the primary magmatic biotite by a slightly higher Mg component (X Mg = 0.53-0.68 compared to 0.62-0.66). This can be explained by the consumption of Fe to form pyrite and chalcopyrite. Chlorite occurs as an alteration product replacing magmatic biotite and hornblende, as well as hydrothermal biotite. Chlorite geothermometry indicates a narrow range between 212 and 246 °C for the formation of chlorites from various alteration zones, implying that the whole system equilibrated with a common fluid at low temperatures.