The operator of the Buckreef Gold Project is Buckreef Gold Corporation Limited, a joint venture that is 55% owned by one of the TRX Gold’s subsidiaries (TRX Gold Tanzania Limited), and 45% owned by STAMICO, a Governmental agency of Tanzania.
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Summary:
Buckreef Gold Project (“Buckreef”) comprises of four gold deposits namely Buckreef, Eastern Porphyry,Tembo and Bwinga all within 4km of each other. Buckreef deposit is the largest of the four deposits of the area.
Buckreef Deposit
The Buckreef Prospect is a shear zone hosted gold deposit within a sequence of mafic basalts and dolerites, near basement granite. The host rocks at the Buckreef deposit comprise primarily pillowed, amygdaloidal and massive mafic meta-volcanic rocks which have been intruded by medium to coarse grained dolerite sills and dykes. Slivers of carbonaceous units have been observed in some drill-core sections incorporated in the metavolcanic assemblages. Minor granitoids (possibly metasomatic) are noted in the north part of the deposit towards the contact with the northern granite.
The mineral assemblage includes py, ± po, cpy, mt with associated silica, carbonate and sericite alteration. Gold is associated directly with sulphides as microscopic inclusions. Sulphides are disseminated and may comprise up to 5% of the rock by volume. The gold mineralization at Buckreef Prospect is non-refractory in both fresh and oxide material. Deep drill-holes indicate that high grade mineralized zones plunge steeply to the north. Several narrow, more discontinuous sub-parallel zones of similar alteration and mineralization have been defined both to the west and to the east of the main fault zone. Detailed logging of drill-hole core reveals a prominent deepening of the oxidation profile above portions of both the Main and North Zones. Superimposed on the host rock is an intensely weathered laterite profile up to 40m depth. Gold may be concentrated in the oxide weathering profile by supergene processes. Fresh sulphides generally do not occur shallower than 40m from surface. The base of the oxidation zone occurs between 15m and 40m, with an average depth of 30m, and the overburden consists of both black cotton soils and lateralized duricrusts with an average depth of ±3m-4m, to a maximum of 20m.
Bingwa Deposit
The Bingwa Prospect is located adjacent to a sheared contact with a granitic intrusive and is approximately 4km east of the Buckreef deposit Gold mineralization has been identified in a drilling program over a strike length of 350m and up to 100m below surface, with the main zone of mineralization occurring over a strike length of 150m. Gold mineralization at Bingwa is associated with quartz veining in strongly foliated and altered greenstone in a shear zone adjacent to the granitoid contact. The shear zone strikes northeast and dips steeply to the northwest. The main zone of mineralization is associated with the junction of a northwest striking, shallowly north dipping fault and the northeast striking shear zone.
Deformation, alteration and gold mineralization appear to be limited to rheological contacts, between basalt and the early quartz veins and along the margin of the granite. The difficulty in constructing continuous grade envelopes may be due to limited continuity of the early quartz vein array, and/or the possibility that the veins are folded, transposed and boudinaged within shear zones. Most the mineralization defined to date occurs within the oxide zone, which extends to 40m-60m below surface. The entire deposit is overlain by 5m to 8m of overburden and transported alluvial. Much of the Bingwa Prospect gold mineralization in the weathered profile occurs in lower saprolite, below the redox boundary. There is negligible upper saprolite below the overburden cover. Given that there is typically limited chemical dispersion of gold in lower mafic saprolite, this may be one of the reasons for poor lateral grade continuity at the Bingwa Prospect. However, recent work at the Bingwa Prospect indicates that mineralization is hosted within the north-northwest to south-southeast trending structures at the intersection with the major northeast-southwest shear zone. The intersection between these structures is considered to play an important role in controlling high grade zones.
Eastern Porphyry Deposit
The Eastern Porphyry deposit is located 0.8km east of the Buckreef main deposit and consists of weakly to moderately sheared felsic porphyry and younger fresh feldspar quartz porphyry dykes up to 30m wide within a mafic sequence dominated by medium grained dolerite. The Eastern Porphyry structures occur within sheared basaltic lavas and medium grained dolerite intrusive of the northeast-southwest trending Nyamazama River lineament. The elongated intrusion attains a maximum thickness of 280m, but thins and disperses to the northeast and southwest into a series of relatively narrow quartz-feldspar-porphyry dykes.
The Eastern Porphyry mineralization is associated with silicified and weakly pyritised shears, quartz veins and veinlets, and within quartz-feldspar porphyry. Quartz veining within the felsic unit may contain pyrite with or without low grade mineralization. However, zones of shearing within the dolerite up to 7m in width are associated with silica-carbonate-pyrite alteration. The mineralization has a total strike length of approximately 1,500m. The main intrusion is coincident with a circular magnetic anomaly in the area with a diameter of 350m (Barrett, 2000). In places the quartz-feldspar porphyry is magnetite bearing, readily deflecting a hand magnet.
The gold mineralization occurs in a similar lithological and structural setting as at Buckreef Prospect, but the intensive carbonate-silica-pyrite alteration typical of the Buckreef deposit is lacking or poorly developed. The fact that mineralization on the Nyamazama River lineament is less well developed than at Buckreef may be due to less dilation of the northeast-southwest shear compared to that of Buckreef Prospect or the presence of the porphyry intrusion which inhibited fluid flow and was less chemically reactive than the basalt.
Tembo Deposit
The Tembo deposit locates approximately 3km southwest of Buckreef Mine, adjacent to the main Rwamagaza Shear Zone. The mineralized zones at Tembo are confined to the east – west trending shears within met-basaltic volcanic package. Alteration in the mineralized zones consists of silica carbonate-pyrite with well-preserved shear fabric.
Gold mineralization is associated with grey quartz thin veins, stringers and boudins parallel to the shear fabric. At Tembo deposit, the transported and residual soil cover is 7m to 9m deep, below which, completely altered and sheared mafic material occurs to a depth of 50m. Most of the oxidised zone has been exploited by artisanal mining.