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The Blackwater camp of central British Columbia

by Virginia Heffernan on March 9, 2012 Discovery

Exploration activity is heating up in the Blackwater gold camp of central BC now that New Gold has consolidated its land position with a 100% interest in the Blackwater and adjacent Capoose properties, both of which contain significant gold-silver resources and lots of blue sky potential.

Another area play to keep an eye on is Greencastle Resources’ Nechako project north of and along the same geologic trend as Blackwater. Nechako and Blackwater both lie within a structurally raised block, called the Nechako Plateau, where mineralization is likely related to the emplacement of Cretaceous intrusives into the Jurassic Hazelton and Bowser Lake Groups.

Last year, Fugro Airborne Surveys flew a detailed heli-borne magnetic and EM geophysical survey for Greencastle. The 1500-line km survey at 100 m line spacings identified 73 high priority anomalies that show favourable structure, magnetic association, conductance and/or size. More extensive conductive zones were given a lower priority because the gold targets at Blackwater are generally non-conductive.

Blackwater is considered to be a low sulphidation epithermal gold-silver deposit. Mineralization is associated with phyllic to potassic or kaolinite alteration of felsic and intermediate volcanic rocks with secondary quartz. The altered volcanic rocks are shot through with pyrite and other sulphide minerals such as sphalerite, tetrahedrite and arsenopyrite. From drilling results to date, New Gold estimates that the discovery contains a bulk tonnage resource of some 6.6 million ounces of gold.

Despite the large quantities of gold, interpreting this style of mineralization can be challenging because the mineralization does not provide a geophysical contrast with the surrounding host rocks, the deposits can be small and geologically complex, and the auriferous vein and stockwork systems tend to be relatively thin and discontinuous. As a result, geophysical interpretation must be able to detect subtle structures that might be controlling gold deposition as well as weak anomalies created by alteration and deposition processes.

To tackle this challenge, Greencastle hired Intrepid Geophysics to undertake a detailed analysis of its survey data to find Blackwater clones. Intrepid has done similar work for other area players such as International Samuel Explorations and Gold Reach Resources and its president, Christopher (Kit) Campbell, worked on the Blackwater property as a summer student decades ago.

By applying enhancement filters to the magnetic grid, Intrepid highlighted a number of dominant structural orientations and trend, including definite breaks in the magnetic fabric that may correspond to lithological boundaries and shear zones.

Intrepid then conducted a profile by profile analysis of the EM data to choose the better conductors, and reviewed them in the context of the magnetic patterns. A variety of geophysical software tools were used to conduct multi edge detection analysis, filtering, image enhancements and analysis. Tools included the CET Grid Analysis extension for Geosoft Oasis montaj which was used to first delineate regions of magnetic discontinuity that correspond to both lithological boundaries and shear zones using a combination of texture analysis and symmetry feature detection techniques. Secondly, the data was examined using fractal analysis to find areas nearby with a complex magnetic expression (zones of structural complexity). The most prospective areas are those where inferred structural complexity occurs adjacent to the regions of magnetic discontinuity. All the GIS work was completed in MapInfo, and the final maps were produced in Geosoft.

“After comparing (the original 73 targets) to what we might reasonably expect from a Blackwater look-alike and depending heavily on the inferred structural context, we pared that down to the final 13 high-ranked targets for follow-up during the forthcoming field season,” says Campbell.

Two significant areas of interest are positively identified by the work done on Greencastle's property, while a third and fourth are implied. Of particular interest, he says, is a magnetic low identified at the southeast portion of Nechako property, as magnetic lows in the region may reflect magnetite destruction in altered mineralized systems.

Campbell believes that the frequency-domain electromagnetics used initially on the Nechako Plateau failed in some instances to penetrate the significant cover of glacial tills and that the better results in the area might be coming from subsequent time domain electromagnetics, including HeliTEM,VTEM and AeroTEM. Geotech’s ZTEM has also been used as an effective tool.

High-priority targets in the gold camp similar to those detected by Greencastle have been further explored with ground IP and resistivity techniques and some correlate with multi-element geochemical anomalies. For many companies, drilling will be the next step to determine if more Blackwater-type deposits can be found. New Gold is certainly optimistic about the camp’s potential.

"The consolidation of our interest in Blackwater and the addition of Capoose further confirm our excitement about the future of the Blackwater project and surrounding area," said Executive Chairman Randall Oliphant when the company purchased area player Silver Quest Resources in late December. "With Blackwater already having a significant gold resource that should continue to grow and a land package now totaling over 670km2, we are excited to move forward with continued exploration and development in this area for many years to come."

Related News:
New Gold Announces Further Increase in Gold Resources at Blackwater Project