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Gold/Mining/Energy : Gold and Silver Juniors, Mid-tiers and Producers -- Ignore unavailable to you. Want to Upgrade?

To: hubris33 who wrote (8862)	4/5/2006 2:04:34 PM
From: E. Charters	Read Replies (1) \| Respond to of 78416

Those are good generalizations of the main theories. Statistically what we know about gold deposits is that they are involved with silica, and accessory minerals of varying concentrations in regimes of certain volcanic rocks that are very similar to the rock formations that contain iron formations and massive sulphide deposits. In fact many major sulphide mines are in fact so high in gold that they can be called gold mines. Most of the gold in Canada for decades came from copper mines, such as the Horne and the Geco, which are no longer operating, BTW. It is generally accepted that the CDN deposits are often relatively sulphide poor, but still sulphidic, multi-phase, carbonated deposits with gold as the last depositional phase, proximal to volcanic vents that are subaqueous and on the margin of either iron formation and/or quartz feldspar porphyry in rocks of a certain temperature. Many of the veins deposit their lode in dilations implying that depressurization caused boiling leading to metal exsolution or precipitation. In others the natural temperature fall of elevated intrusion cause gradual precipitation of solution, which had the added effect of nucleation at sites of previous metal deposition electrochemically. When arsenic exsolved from solutions on contact with iron either in oxide, or sulphide form, or in contact with sulphide gas phases, in a mixing environment where existing previous deposits were dissolved or melted by hot pressurized gas, the solubility of gold decreases by 50 times. Ergo, exsolution of precious metal. "The reason why some districts or specific rock formations are so prolific and contain major Au-VMS deposits adjacent to gold-poor VMS deposits remains one of the most critical questions to be addressed. The best example in point is the Archean Blake River Group of the Abitibi subprovince. The Blake River Group contains 682 metric tonnes of gold, which represents 80% of the production and reserves for this sub-type of gold deposits in Canada, and 25% of the known gold in the Abitibi greenstone belt. The Blake River Group is, therefore, a particularly important exploration target for this style of gold deposit (Dubé; et al., 2003). The Blake River Group also hosts many conventional VMS deposits. The reason(s) why these rocks are so prolific and contain such major Au-VMS deposits has been the subject of recent collaborative work in the Doyon-Bousquet-LaRonde district (Lafrance et al., 2003; Dubé; et al., 2004; Mercier-Langevin et al., 2004). The geochemical composition and volcanic facies of the Au-VMS hosting Bousquet Formation of the Blake River Group, as well as the geological setting, are key elements responsible, at least in part, for the formation of the district. However, more work remains to be done to fully understand the unique gold endowment of this particular volcanic group. As proposed by Hodgson (1993) and by Huston (2000), it is also possible that the "provinciality" of the high Au grade of the VMS deposits may be related to specific fundamental geological characteristics in terms of favourable source-rock environments or gold-reservoirs. The local geological "heritage" (endowment) of the district, in addition to ore-forming processes, may indeed be a major factor to take into account."