Tuesday, March 22, 2011

A Short Guide To Epithermal Deposits

Epithermal deposits are formed by heated subsurface water carrying gold into veins. Many of those hydraulic sources get their heat from nearby magma, but some just get it with ground water.
Gold is the principal commodity of epithermal deposits, and can be found as native gold, or alloyed with silver. As a lode deposit, epithermal deposits are characterized as having minerals either disseminated through the ore-body, or contained in a network of veins. Beyond epithermal deposits, other classic examples of lode deposits include Greenstone Belts, VMS and Intrusive Related Gold. Epithermal deposits are distinctive from low-grade bulk tonnage deposits such as porphyries in that they are typically high-grade, small size deposits.

A few characteristics distinguish epithermal deposits. These deposits are found near the surface and mineralization occurs at a maximum depth of 1 km, but rarely deeper than 600 m. Due to their shallow depth, it can also be noted that epithermal gold deposits form under moderate crustal temperatures of 50-300oC, and under medium pressure. These deposits commonly occur in island arcs and continental arcs associated with subduction. However, they can also be found in shallow marine environments and associated with hot springs. Due to their shallow-depth location, epithermal gold deposits are more susceptible to erosion; accordingly, these deposits represent a high-grade, easily mineable source of gold.
The guide goes into the possible origins of those deposits and contains a list of five mining or exploration companies with epithermal deposits.

One junior explorer that has a knack for finding epithermal deposits is Alexandria Minerals. It had ownership or rights to 21 properties in the Cadillac Break area of the Abitibi Greenstone belt in Quebec. Its flagship property is the Sleepy.

Unfortunately, the properties with deposits only possess small ones. That's why Alexandria's stock has been a plodder this past year.

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