Morabisi North/Kamawari Project

In late 2000 an investigation was made of the area north of the 1999 Morabisi Project area. The purpose of the work done was to establish if a multi-element geochemical anomaly extends to the north along major structures seen on aerial photographs. A second objective was to investigate columbite/tantalite occurrences recorded from the headwaters of Kunaballi Creek in the south-east of the area, and the final objective was to investigate if gold mineralisation exists away from previously known areas such as Peter’s Mine on the Puruni River.

Work done included regional multi-element geochemical sampling and geological mapping. Fieldwork was done in November and December 2000. Samples collected included 134 bulk –30# sediment samples, 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 883 sq. km. (one site per 6.5 sq. km). 46 rock samples were also taken. –30# BLEG samples splits (2kg) were analysed for Au, Ag, Pt and Cu, and –80# samples and rock samples analysed for “Au+48” using NAA and ICP in Canada. Fourty rock
samples were examined petrologically.

Prior to the start of fieldwork, a GIS database was set up, including 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 Barama-Mazaruni Supergroup metamorphic rocks intruded by Younger Granites. Both these units are intruded by Younger Basic sills and dykes. The age of smaller acid intrusions which appear to be associated with gold mineralisation in the area is unclear; these could either be intrusions related to the Barama-Mazaruni Supergroup, where alteration has obscured metamorphic effects, or be related to of the Younger Granites. Older geological maps suggest that Bartica Assemblage high grade metamorphic rocks should be present in the western part of the area. No evidence was seen for the presence of this unit.
Examination of old maps showed no structural data, suggesting that this unit may have been mapped from air photos. Some of the Younger Granites show evidence of foliation related to syn-fault intrusion.

Geochemistry has shown that the known area with gold mineralisation in the NE of the area, which includes Peter’s Mine and Million Mountain, extends at least 30km westward. Almost all sites draining the area with Mazaruni Group metamorphic rocks north of the old road contain appreciable amounts of gold in either the stream sediment, pan-concentrate or BLEG sample.A distinct arsenic-antimony anomaly is also present in this area. The style of possible primary mineralisation could not be identified from field evidence, but Peter’s Mine consists of a N-S quartz vein zone, while at Million Mountain a stockwork quartz vein zone as well as a Au-bearing manganiferous low angle fault zone are present.

An annular zone with tantalum anomalies in stream sediments correlates approximately with the distribution of Younger Basic rocks. Tantalum values are similar to those seen in the Morabisi area, where alluvial columbite-tantalite was mined, suggesting that a similar, but untapped resource may be present . The association with basic rocks remains a mystery. Usually columbite and tantalite occur in pegmatites. One possibility is that the Morabisi Batholith is Ta enriched, and that pegmatite veins formed as a result of partial melting after intrusion of the basic rocks. The presence of stream sediment Ta anomalies in the headwaters of the Potaro River
(Pakaraima Project – report in compilation), in drainages where only basic sills occur, suggests that a more direct relationship between Ta and basic rocks is present. Thin sections of these basic rocks often show the presence of a late differentiate of quartz, biotite and opaques.

Repeat sampling of the original multi-element anomaly in the north of the Morabisi area resulted in a similar, but lower assay. However there is no obvious continuation to the north. No mineralised rock outcrop or float could be found, and it is concluded that the original anomaly is probably related to a small zone of fault hosted mineralisation of no significance.

No significant base metal mineralisation was identified. This matches the conclusions reached after previous work under a United Nations programme in the NE of the area. The UN hoped to find volcanogenic massive sulphides by drilling EM anomalies, most of which proved to be related to carbonaceous horizons in meta-sediments.

The significance of smaller areas with Pt and Pd BLEG anomalies is not clear. Most of these appear to be related to areas of meta-basic rocks within the Barama-Mazaruni Supergroup. In one of these catchments 1450ppm Cr is also present, suggesting the possibile presence of metamorphosed gabbroic cumulate rocks.

Much of the north and east of the area examined is covered by valid Medium Scale Prospecting Permits, but the western end of the gold anomalous zone is not currently claimed. In the SE of the area near known alluvial columbite-tantalite mineral occurrences, again much, but not all of the area is claimed. In the west of the area the Ta anomalous zone is unclaimed. Currently the area is closed for applications, and remaining areas will be offered to the public through public auction.

The following diagrams summarise available information.

Mineral Ocurrence Map (303K)
Geological Summary Map (354K)
Au Anomaly Map (322K)
Tantalum Geochemistry Map (323K)
Auction Blocks Map (325K)

REFERENCE : Heesterman, L.J.L., Kemp, A.W. & Nestor, G. 1999. Morabisi North / Kamawari Project A Summary of Geochemistry, Geology and Structure. Guyana Geology and Mines Commission, Geoservices Division Technical Report GS1/2000.