Espectrometría Raman y microtermometría de inclusiones fluidas en cuarzo magmático e hidrotermal en los pórfidos de Cu-Mo de Lucy y María, Sonora, México
The Lucy and María ore deposits are found within the Laramide belt or porphyry copper deposits in northeastern Sonora, their tonnage is medium-sized, and produce copper with subordinate molybdenum. The ages of the intrusions associated with the ores range between 64 and 67 Ma. Hydrothermal alteration developed on pegmatitic intrusives and consists mostly in pervasive quartz-sericite assemblages with associated chalcopyrite and molybdenite. Ores are essentially hypogene with weakly developed supergene enrichment. At the Lucy deposit, both magmatic and hydrothermal gangue quartz crystals associated with the copper-molybdenum ores bear the same types of fluid inclusion associations (FIA), with vapor-rich (V) and liquid+vapor (L+V) inclusions coexisting with S1-4+L+V type inclusions, thus constituting evidence for boiling. Their analysis by means of Raman microspectroscopy confirms that S1 = halite, S2 = hematite, S3 = molybdenite, and S4 = pyrosmalite-(Fe), all of them being daughter crystals from magmatic brines. Eutectic temperatures in L+V inclusions in granodiorite quartz fenocrystals las inclusiones de tipo L+V are ~ -35 °C, which may correspond to H2O-NaCl-MgCl2 and/or H2O-FeCl2 systems; ice melting temperatures indicate salinity ranges between 26 and 23 wt. % NaCl equiv., and temperatures of homogenization to the liquid phase (Tll) vary between 550 ° and 240 °C at 760 bars. S1-4+L+V fluid inclusions due to magmatic fluids systematically display vapor homogenization into liquid (Thv) at a temperature range between 260 ° and 265 °C, followed by halite solubilization (ThfNaCl) between 520 ° and 550 °C, thus corresponding to salinities between 55 and wt. 63 % NaCl equiv. and featuring an obvious decompression process. Al the above implies that the ores at Lucy were emplaced at ~3 Km and are interpreted here as the earliest and deepest bodies in the Cananea district, in association with a batholithic complex instead of hypabyssal porphiries, and were exposed at the surface due to the rotation of the Cuitaca semigraben. At the María deposit, both magmatic and hydrothermal quartz crystals contain L+V and L+V+S1-4 type fluid inclusions. The L+V inclusions analyzed through Raman microspectroscopy yield volatile contents of CO2 (81% mol), CH4 (0.5% mol), H2S (1 % mol) and H2 (17.5 % mol). The daughter crystals observed in multisolid inclusions (S1-4+L+V) are S1 = halite, S2 = magnetite, S3 = chalcopyrite, and S4 = pyrosmalite. The salinities of L+V inclusions range between 13.9 and 19.9 wt. % NaCl equiv., temperatures of homogenization between 408 ° and 510 °C, and a minimum pressure of 590 bars. The salinities of S1-4+L+V fluid inclusions (interpreted here as part of the magmatic protofluid) range between 30 and 42 wt. % NaCl equiv., and temperatures of homogenization between 250 ° and 400 °C. It is interpreted that ore formation occurred due to drastic decompression (down to 130 bars) and late dilution of ore-bearing fluids (possibly due to mixing with meteoric water), which took place after initial boiling in response to rapid emplacement of the mineralizing intrusive.