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Gold/Mining/Energy : Flag Resources (FGR.A A) -- Ignore unavailable to you. Want to Upgrade?

To: RJ2 who wrote (4078)	11/7/2003 2:21:50 PM
From: ali	Read Replies (1) \| Respond to of 4269

From a report by Dr.Eva Schandl, consulting geologist research associate, Dep. of geology Uof T. DISCUSSION AND CONCLUSIONS (1) The present fluid inclusion study demonstrates that the fractured and brecciated quartz veins and qu~rtz-rich pods with pyrite aggregates at Cobalt Hill crystallized from chloride-rich brines. The significance of chloride-rich brines is, that they mobilize and carry metals as chloride complexes. Such scenario has been described at the Sudbury Igneous Complex by Farrow and Watkinson (1992) and Jago et al. (1994); at the Merensky Reef of the Bushveld Complex by Ballhaus and Stumpfl (1987), at the New Rambler mine by Wyman et al. (1990) and at the Lac des lies Complex by Tellier et al. (1991). Results of this study suggest that the fluids that crystallized the quartz veins and pyrite at Drill hole DOH 92-1 and its vicinity, were similar to late-magmatic flurds dpcumented at the Sudbury Igneous Complex and at other Ni-Cu-PGE deposits. The ubiquitous occurrence of small inclusions of gersdorffite, bravoite, pentlandite, chalcopyrite, pyrrhotite, Hg-telluride (coloradoite) and some gold in pyrite (Table 1) in the quartz veins at Cobalt Hill is 'evidence for the mobilization of metals by the chloride-rich solutions. The predominance of Ni-sulfides and chalcopyrite inclusions in pyrite at Cobalt Hill suggests that the source of these fluids must have been Ni and Cu- rich, whereas the previously reported occurrence of fuchsite in the same quartz + pyrite veins implies that the source of metals (and Cr in the fuchsite) was probably a mafic- ultramafic intrusion at some (not too distant) depth. (Schandl, February, 2002). (2) Fluid inclusion microthermometry demonstrates the strong similarities between late-magmatic fluids of the Deep Copper Zone of Strathcona mine and the fluids that crystallized the Cobalt Hill quartz veins. Homogenization temperature, salinity and the presence of halite daughter minerals in fluid inclusions in quartz veins at Cobalt Hill are comparable to the temperature and salinity of fluid inclusions in quartz at the Deep Copper Zone of the Strathcona mine (Farrow and Watkinson, 1992). In addition, the -- 7 pressure-corrected crystallization temperature for the Cobalt Hill quartz veins is in the range of 175°- 325°C, and the pressure-corrected crystallization temperature for quartz in the Deep Copper Zone was estimated at 175° to 280°C by Farrow and Watkinson (1992). The salinity of the Cobalt Hill inclusions are also comparable to the salinity of fluid inclusions in quartz at Barnet and at the epidote zone of the Fraser mine (Farrow and Watkinson, 1992). Table 2 summarizes and compares similarities in temperature and salinity between the Cobalt Hill fluid inclusions and fluid inclusions from the North Range deposits of the Sudbury Igneous Complex. (3) On basis of the present fluid inclusion and earlier mineralogical study, I consider Cobalt Hill to have an excellent potential for Sudbury-type mineralization. The quartz + pyrite veins originated at relatively shallow depths of maximum 1 kb (ca. 3km) (as estimated from the CO2-H2O fluid inclusions) by chloride-rich brines that carried various Ni-Cu sulfides and gold, all of which are included in pyrite within the quartz veins. This depth is comparable to the (shallower) estimated depth of ore-formation for the North Range (3-8 km: Farrow and Watkinson, 1992). Uplift and erosion must have since reduced this depth considerably. The present study demonstrates the existence of a hydrothermal system at Cobalt Hill that is known to be characteristic of certain types of ore deposits. Metal- carrying chloride-rich brines are commonly associated with porphyry-type deposits on the global scale, as well as with Ni-Cu-PGE-type deposits. While a porphyry system cannot be ruled out at this stage, the occurrelJce of fine-grained Ni & Cu sulfide inclusions in pyrite would favor Sudbury-type mineralization for the vicinity of Cobalt Hill. As sodium metasomatism in the area post-dated the quartz veins + pyrite, as well as brecciation at Cobalt Hill (Schandl, February 2002 report), the quartz veins must be older than the reported age of sodium metasomatism in the area at 1700 Ma (Schandl et alo, 1992), but significantly younger than the Lorrain quartzites.