Upper Puruni ProjectThe Upper Puruni, downstream from Majuba Hill /Wynamu confluence has a long history of alluvial gold workings from the 1930's to the present, and mining with 9 dredges was underway in that area during the period of the field programme. This project was designed to investigate the extent of gold mineralisation in the area, and to determine whether any other types of mineralisation occurs. Methods used included regional geochemical sampling, geological mapping, thin section description and air photo interpretation. Fieldwork was done in Feb-Mar 2000, with geochemical samples collected from 110 drainage sites.
The area is underlain by sedimentary, metamorphic and intrusive rocks of the Mazaruni, Barama and Bartica Groups, intruded by Younger Granites. Younger basic intrusives of possible Mesozoic age are also present with a few areas of Plio-Pliestocene White sand. Interpretation of aeromagnetic data indicates a number of major structures/faults and it is postulated that mineralisation may be associated with these. 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.Fieldwork showed that at least some of the alluvial gold was derived from strongly potassic-altered granitic rocks, and in some places was associated with quartz veins in greenstones. Magnetite and epidote skarn float indicates other mineralisation styles are also present, together with limited occurrences of volcanic exhalative mineralisation. Mapping has generally confirmed lithologies shown on previous maps, with phyllites, quartzites and other meta-sediments occurring to the north of the meta-volcanic / greenstone unit.
Geochemical results confirm that high Au assays occur in the Toroparu or Majuba Pit area, and this includes both rock samples, saprolite from the pit, as well as drainage samples upstream of the main pit. Hardrock mineralisation as well as alluvial gold are clearly present. This area is the obvious target for further exploration to establish the tenor, areal extent and depth of mineralisation. This area is covered by valid Medium Scale Prospecting Permits (PPMS).
Drainage gold geochemistry suggests that there are a number of other gold anomalous areas outside of the immediate Majuba pit area. One area with up to 1.8ppm Au in stream sediments occurs approximately 10km further north. A gold anomalous zone ( max 0.3ppm Au in SS & 1ppm in rock) strongly associated with high arsenic (up to 4130ppm in rocks and 32.2ppm in SS), occurs in the north east of the project area. This anomaly is related to a major NW-SE shear zone, and possibly to the nearby Aurora Granite. Rock samples with very high manganese (max153700ppm), but no significant gold, occur in a breccia zone at the western end of the high As/Au zone. These rocks may represent re-mobilisation from manganiferous volcanic exhalative mineralisation ('black smokers'). The Guyana Geology and Mines Commission auctioned five Prospecting Licences over the northern and NE Au anomalous zones in July 2001.
High chromium and nickel in SS and maghemite in HMC suggests the presence of unmapped ultra-mafic rocks in the headwaters of the Putareng River.
The following diagrams summarise available information.
Aeromagnetic Summary Map (113K)
Geological Summary Map (165K)
Mineral Occurrence Map (130K)
Au Geochemistry Map (129K)
Auction Blocks Map (139K)REFERENCE : Heesterman, L.J.L., Kemp, A.W. & Nestor, G. 2001. A Summary of Geochemistry, Geology and Structure in the headwaters of the Puruni River. Guyana Geology and Mines Commission, Geoservices Division Technical Report.