Characterization of the geological and geo-chemical footprint of the Koolhoven gold deposit, Suriname.

Characterization of the geological and geo-chemical footprint of the Koolhoven gold deposit, Suriname.

Carlier, L.C.F.

Buxton, M.W.N. (mentor)

Civil Engineering and Geosciences

Geoscience & Engineering

Resource Engineering

2012-12-12

Characterization of the geological and geo-chemical footprint of the Koolhoven gold deposit, Suriname. IAMGold operates Rosebel N.V. Gold Mines in Suriname, South America. The producing deposits are characterized to be Archaen greenstone hosted quartz-carbonate vein deposits. Regional exploration projects are located in rainforest environment. Geologists are therefore confronted with difficult access, few outcrops and deep weathering. Efficient exploration is crucial and for this reason a profound understanding of the local geology, gold depositional mechanism and signature is required. There is a hypothesis that a temperature gradient resulting from the flow of hydrothermal fluids through the shear and tension veins will have caused alteration halos to be formed around the gold deposit. Specific element enrichment and depletion are also expected near the gold deposition as a result of changing pressure/temperature regime and fluid characteristics. Recognizing and understanding alteration halos will increase the target area in an exploration campaign. To test this hypothesis 28 boreholes with a maximum downhole depth of 230 meters were sampled across the producing Koolhoven pit on the Rosebel concession. 85 Samples were analysed for trace element and major element content in a laboratory. 904 Samples were analysed using an X-50 Mobile XRF device for element content. 1573 Spectral measurements were obtained using a Hi-Res Terraspec and 40 thin sections were analysed using a conventional polarization microscope and electron microprobe. The petrographic analysis reveals the presence of quartz, carbonate, chlorite, pyrite, chalcopyrite, magnetite, hematite, rutile, clay mineral and feldspar including plagioclase. Bleached veins selvages are associated with high concentrations of carbonate and sericite, pyrite porphyroblasts and are devoid of chlorite. The sulfide mineral content does not exceed 5%. The conglomerate clasts are identified to be of volcanic origin mainly, hereby supporting the major element results. The veins contain quartz, carbonate, chlorite and the accessory minerals white-mica and tourmaline. Due to the low degree of deformation the veins are concluded to be of late timing compared to the main deformation. The use of major element analysis has resulted in the effective differentiation of lithologies present in the Koolhoven pit. Siltstone/mudstone, two types of greywacke (A and B), sandstone, conglomerate and volcanic rock ranging from mafic to felsic have been recognized. Greywacke B and conglomerate are spatially related and their major-element content resembles that of the volcanic rock. The use of log-ratios to analyse the trace element data suggests the presence of correlations between specific element ratios and gold concentrations. The best results were obtained by analysing one borehole a time. Different correlations are suggested in the different boreholes. It therefore remains uncertain to use the presented results for the entire deposit. The visible and near infrared spectral analysis reveals that paragonite, Fe-chlorite and carbonate are the dominant minerals encountered. No direct link has been found between specific minerals, mineral crystallinity and relative mineral proportions to gold concentrations. Volcanic rock is devoid of muscovite. The presented results of the identified lithologies are in accordance with the regional geological evolution. The alteration characteristics determined are to be considered as the proximal alteration zone of the Koolhoven deposit. Up to a distance of 500 to 1 km away from the gold mineralization no alteration halo has been found except from the small scale bleaching near veins. Since the characteristics described in this report represent the proximal alteration, they may be used in exploration campaigns to define if hydrothermal fluids have been flowing in the area and hence there is a chance of gold deposition.

gold
alteration
XRF
Suriname

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Student theses

master thesis

(c) 2012 Carlier, L.C.F.