CEO Blog - Jan 27, 2011
Thursday, January 27 2011 15:10
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Question: Why is quartz porphyry important in The Comstock?

Answer: In our Lucerne Resource Area, quartz porphyry is one of the more favorable hosts for mineral enrichment by mineralizing fluids, and in places, can be very thick.

This typical east-west cross section, looking north, shows an example of the intruded quartz porphyry, represented by the orange hatching, filling most of the space between the Silver City and Gold Canyon faults.  Higher gold grades, shown in red, are seen to be concentrated in the quartz porphyry.

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Typical Lucerne Cross Section

In specific locations, the intrusive is seen to have replaced the entire zone between two of the sub-parallel faults, creating mineralized zones over one hundred feet in thickness.

The traditional view of the geology in the Lucerne Resource Area is as a layer-cake of volcanic rocks.  At the bottom, is the rock we call the meta-volcanic unit.  This is a thick sequence of volcanic rocks, approximately 180-200 million years old, which were metamorphosed by heat and pressure, and then partially eroded.  On top of this erosional surface (geologically, an "unconformity"), younger layers (18-24 million years old) of volcanic ash (tuffs) and volcanic flows (andesites and rhyolites) were deposited.

This layer-cake was faulted by the northwest trending Silver City fault zone, a series of sub-parallel faults, and faulted again by northeast and north-south trending faults.  In the traditional view, the faults created pathways for the mineralizing fluids which enriched the surrounding rocks.  As we have seen in our exploration-drilling program, enrichment can occur along any of these faults, and in any of the rock types, although some rock types are more receptive, and tend to host thicker intervals of enrichment.

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Actual chip tray and corresponding gold & silver assay results

Our new twist on the geology of the Silver City fault zone is that the sub-parallel faults created fractures that resulted in zones of weakness, especially along intersections with the northeast-trending faults.  The weaker zones created pathways for the quartz porphyry to intrude, replacing the existing rock.  Needless to say, when our drilling exposes extended instances of quartz porphyry, it’s a very good sign.

Kindest regards,

Corrado De Gasperis
President and CEO