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ALTERATION AND MINERALIZATION IN THE RAIGAN PORPHYRY SYSTEM, IRAN: EVIDENCE FROM FLUID INCLUSIONS
Abstract
The Raigan porphyry copper system is located in southeastern Iran (Kerman province), and is associated with diorite/granodiorite to quartz-monzonite of Miocene age that intruded Eocene volcano-sedimentary rocks. Copper mineralization was accompanied by mainly phyllic and lass potassic alteration. Field observations and petrographic studies demonstrate that emplacement of the Raigan stock took place in several intrusive pulses, each with associated hydrothermal activity. Molybdenum is not reported in any stage of hydrothermal evolution through the system. Due to lack of information, the petrogenesis interpretation is mainly based on the field observation. It seems that early hydrothermal alteration produced a potassic assemblage (orthoclase-biotite) in the central part of the stock, propylitic alteration occurred contemporaneously with potassic alteration, but in the peripheral parts of the stock, and phyllic alteration occurred later, overprinting all the earlier alteration (the most majority alteration in the Raigan system). The early hydrothermal fluids are represented by high temperature (487 oC to 598 oC), high salinity (up to 61.1 wt \% NaCl equiv.) liquid-rich fluid inclusions, and high temperature (397 oC to 401 oC), low-salinity, vapor-rich inclusions. These fluids are interpreted to represent an orthomagmatic fluid which boiled episodically; the brines are interpreted to have caused potassic alteration, containing first generation of chalcopyrite. Propylitic alteration is attributed to a liquid-rich, lower temperature (523 oC to 298 oC), Ca-rich, evolved meteoric fluid. Influx of meteoric water into the system, and mixing with magmatic fluid produced deep albitization, and shallow phyllic alteration. This influx also caused dissolution of early formed copper sulfides and remobilization of Cu into the sericitic zone where it was resystemed in response to a boiling-induced decrease in temperature. Supergene alteration was minor and restricted to a thin blanket of Cusulfides.
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temperatures was ±0.2 oC at -56.6 oC (triple point of CO2), ±0.1 oC at 0 oC (melting point of ice), ±2 oC at 374.1 oC (critical homogenization of H2O), and ±9 oC at 573 oC (alpha to beta quartz transition). The heating rate was approximately 1 oC/min near the temperatures of phase transitions. Low temperature phase changes The temperatures of initial (T e) and final melting of ice (Tmice) were measured on types
LV, VL and LVHS fluid inclusions. In the case of type VL inclusions, T e was difficult to determine, because of the high vapor/liquid ratios. Clathrate formation was not observed in any of the inclusions, which rules out the presence of significant CO2. The crushing of quartz under anhydrous glycerine confirmed this conclusion; the vapor bubble collapsed during crushing in all but a few inclusions, and in the latter inclusions the bubble size was unchanged on increased slightly, indicating that the maximum pressure of incondensible gases was ~1 bar. The temperature of initial ice melting (T e) of most LV fluid inclusions was between -23 o and –24.2 oC, suggesting that NaCl ± KCl are the principal salts in solution. The Tmice values for these inclusions range from –5.1 o to –8.2 oC (Table 1), corresponding to salinities of 5.7 wt. % NaCl equiv., respectively (Sterner et al., 1988). A small proportion of very small (<2 µm ) LV inclusions in quartz phenoc rysts in shallow dykes have T e between -25 o and -39 oC, suggesting the presence of appreciable CaCl 2-FeCl2- MgCl2 in addition to NaCl and KCl, which I did not report it in the table 1 because of the size (Hezarkhani, 1997). The T e value of VL fluid inclusions ranges from –19.7 o to –46.1 oC with a mode of ~-
oC suggesting that Na and K are the dominant cations in the solution but that there are International Conference
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