Kuribrong ProjectIn late 2001 an investigation was made in the upper catchment area of the Kuribrong River. The purpose of the investigation was to investigate the mineralisation potential of the area using multi-element geochemical sampling and geological mapping. Part of the southwestern portion of the project area may in the future be flooded if the Amalia hydroelectric dam project goes ahead. Small scale mining of gold and diamonds, beginning at about 1898 still continues at a number of locations. A geological investigation of an area surrounding and including a major portion of this project area in 1971 encountered evidence of over 100 small gold mining operations (Gibbs 1971).
Work done included regional multi-element geochemical sampling and geological mapping. Fieldwork was done in August and September 2001 Two hundred and sixteen (216) bulk –30# sediment samples were taken using a flocculent, with a –80# fraction separated in the laboratory. At most sites a pan-concentrate could be collected, and was inspected in the field for the presence of visible gold. The area investigated is 2,011 sq. km. (an average of one site per 9.36 sq. km). Sixty-five (65) rock samples were also taken. –30# BLEG samples splits (2kg) were analysed for Au, Ag, Pt and Cu, and –80# samples and rock samples (15) analysed for “Au+48” using NAA and ICP. Forty-five rock samples were examined petrologically.
Prior to the start of fieldwork, a GIS database was set up, which included scanning of relevant geological maps. All outcrop data recorded by previous workers was compiled. Together with fieldwork information, and a detailed air photograph lineament analysis, this has resulted in production of a geological fact map, detailing outcrop lithology and structural information, and a new digital geological and structural map of the area.
The geology of the area consists of Lower Proterozoic Mazaruni Supergroup (aka “greenstone belts”) consisting of meta-sediments and meta-volcanic rocks, intruded by Younger Granites. Uncomformably overlying these rocks is the Roraima Formation, a generally flat lying series of conglomerates, sandstones, shales and volcanics. All of these rocks (greenstones, granites, and post-orogenic sedimentary series), are intruded by doleritic and gabbroic dikes and sills (the Younger Basic Intrusive Suite).
Stream sediment data from this study show several areas of alluvial gold potential that are in agreement with those identified by earlier workers. One new area of potential gold mineralisation was identified east of Ipobe Creek (Figure 3). In the area that would be flooded by the proposed Amalia Falls hydroelectric dam, little evidence of significant gold mineralisation was found, but small scale workings for diamonds are present.
Geochemical data from this study shows some areas worthy of further investigation for other elements. Elevated BLEG copper values occur associated with a northeast trending structure that extends from the Roraima Formation-Mona Gabbro contact south of the Curetoma River northward to the meta-sedimentary wedge south of the Hubana River. A number of other sites have anomalous Cu values, but with no discernable association with a particular lithology or structure. Tungsten occurs in moderate to appreciable amounts in drainages associated with the Apanachi Granodiorite in the northeast part of the project area. Where the Curetoma Granite is surrounded by a ring of gabbroic rock, a number of elements show higher than expected concentrations: Cu, Ti, Ag, As, Se, Ni, Cr, Ta and Hf. Most of these increased concentrations are near the margin of the granite, or are on the contact of the granite with the gabbro. These data may indicate a mineralisation event, possibly coincident with the younger basic intrusion. The nature, extent and significance of this event is unknown.
The following diagrams summarise available information.
Mineral Ocurrence Map (245K)
Geological Summary Map (738K)
Structural Summary Map (1065K)
Au anomaly Map (261K)
Auction Blocks Map (703K)REFERENCE : Cole, E.C., Heesterman, L.J.L. & Kemp, A.W. 2003. Kuribrong Project. A summary of geochemistry, geology and structure.Guyana Geology and Mines Commission, Geoservices Division Technical Report GS1/2003