Platinum mineralization in the Kapalagulu Intrusion, western Tanzania

摘要: Low-grade copper and nickel mineralization was found near the eastern shore of Lake Tanganyika at Kungwe Bay in early part twentieth century. The occurs harzburgite base a layered gabbro complex known as Kapalagulu Intrusion, emplaced between Paleoproterozoic Ubendian basement overlying Neoproterozoic Itiaso Group metasediments. Several mining exploration companies continued geophysical drilling for metals throughout last century culminating discovery high-grade platinum-group element (PGE) associated with chromitite sulfide-bearing within southeastern extension Intrusion (known Lubalisi Zone) that is covered by layer nickel-rich laterite regolith. poorly forms >1500 m-thick Lower Ultramafic Sequence resembles dike-like body flares upwards into succession well-layered gabbroic rocks Upper Mafic Sequence. No PGE has been gabbro; all chromite- sulfide-rich regolith mineralized harzburgite. Zone underlain basal dunite overlain an interval troctolite this ultramafic sequence folded syncline plunges towards northwest modified major dolerite-filled faults orientated subparallel to fold axial surface. Extensive deep shows can be subdivided lower feldspathic harzburgite, containing seams intervals sulfide chromite Main Chromite Sulfide Succession (MCSS), upper Impersistent, stratiform horizons occur MCSS from which drill core samples were taken mineral (PGM) characterization two holes. Where reefs reach surface there residual various lithological units PGM characterization. As contain significant concentrations both (including seams) they resemble PGE-rich Bushveld Complex rather than PGE-bearing Great Dyke Layer Munni Complex. dominant Pd three reef varies, ranging (n = 164, relative wt%) bismuthides (63 %), bismuthtellurides (19 tellurides (6 (39 (24 stannides (14 alloys (13 antimon-arsenides (33 (21 (17 (10 %). From 13.5 % 21.0 total solid solution pentlandite. have similar Pt modal distributions 172, wt%); sperrylite (79, 58, 47 %) followed (15, 17, 21 (2, 1, 1 sulfides 0 Comparison Pd/Pt ratios assays those calculated minerals show data are very robust, confirming concentration methodology Study shallow hole penetrating primary not survived oxidation, mainly dispersed, but some reconstituted form secondary minerals: cabriite, unnamed tellurides, selenide, Pd-Te-Hg mineral, Pd-bearing (millerite heazlewoodite). more resistant oxidation dissolution, especially isoferroplatinum, it likely other (tetraferroplatinum tulameenite) origin after dissolution tellurides.