MAPPING AND SAMPLING TECHNIQUES
During the course of my reconnaissance in Niger, I attempted to make accurate site maps of many of the artesianal prospects I visited. The purpose was to establish local structural trends, rock types, metamorphic grade, alteration, and mineralized rocks and structures. At the time of my visit, there were no large scale topographic base maps or easily obtainable aerial photography. At each site, prospect maps were surveyed with a tripod mounted Brunton compass and distances measured with a metered, hip mounted string box. All surveys were closed and RMS errors distributed among all survey points. I transferred my field maps to mylar after my return.
In that this was a reconnaissance traverse I made an attempt to “high grade” all of my samples. This departure from representative sampling was taken with the assumption that if I could not select anomalous samples in the short time I was present at each prospect, it would be assigned a lower priority for resampling at a latter date. Access to the many deep pits excavated by the artesianal miners was by climbing rope, rappel ring, and Jumar Ascenders.
Coarse gold in this weathering environment is the rule thus I anticipated a severe “nugget effect” and took samples that were 2 kg minimum size and in some cases, 4 kg. Samples were shipped to the BHP laboratory in Bamako for analysis for Au and As by the standard techniques being applied for Syama Project Reconnaissance. Sub samples were shipped back to the United States where I examined and described those that weren’t lost in shipping.
In addition to mapping and sampling, I conducted numerous interviews with artesianal miners at active sites and offered advice when asked. The local miners were an invaluable source of practical information regarding the distribution of gold, directions to active and inactive sites in the region, and short term paid labor to transport samples back to my vehicle.
During my reconnaissance, I engaged Mr. Chris Marion of BUGECO as a consulting geologist to conduct the sampling. My activities were also supported by the Ministry of Mines and Energy from whom I rented a vehicle and engaged a driver.
SIRBA RIVER BELT
The Sirba River Belt is the largest of the schist belts (~5,000 km2), the best exposed, the most pyritic, and has the most known gold anomalies (16 or 17). The area of the proposed reconnaissance concession is defined in map 3. The general trend of the known anomalies defines a line oriented at 60°, sub parallel to the elongation of the belt and to the strike of the foliation. In contrast the bedding in the few places that it can be recognized strikes 80-110º. A variety of styles of mineralization are present. Al Mani Gountou and Boubene are mineralized ductile shear zones, the former with moderate to sparse pyritic quartz veining; the latter with sparse to absent quartz veining and abundant disseminated pyrite. Mbanga, Kundulundou, Libiri North, Kokoloukou, and several other small prospects are all single, simple pyritic quartz veins with highly altered wall rocks and moderately developed pyritic quartz stockworks. Deba consists of pyrite-albite(?)-quartz stockworks adjacent to a fault. Libiri is an extensive pyrite-quartz stockwork of vague trend in highly altered wall rock which could be an alkaline intrusion. Tchalkam consists of many areas of small quartz veins and pyrite-quartz stockworks along a linear trend.
Exploration in the area by local miners, the government, and aid agencies has been directed toward quartz veins. Never the less, good anomalies are known in rock with disseminated pyrite and pyritic quartz stockworks. The potential for further discoveries is high since most of the area has been covered by local miners who use primitive extraction and exploration methods. Exploration has been going on for fewer than 10 years, and people have only worked surficial zones with gold grades above 1 or 2 g/t. Anomalous gold values lower than 1 g/t are ignored. Moreover, no one has tested the potential for large low grade disseminated pyrite ore bodies or high grade primary deposits at depth.
Sirba River Reconnaissance Map
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Sirba River reconnaissance traverse |