Re-Evaluation of Kombat-Style Mineralization and Implications for Exploration in the Otavi Mountainland, Namibia

This study re-evaluates the characteristics of Cu-Pb-Ag and Fe-Mn ore mineralization of the Kombat Mine and Gross Otavi Mine based on field geology, fluid inclusions, petrology, mineralogy, and geochemistry. This is to determine the genetic relationship between Fe-Mn and Cu-Pb-Ag mineralization. The study has established that the Cu-Pb-Ag ore at the Kombat Mine can be classified as a variant of MVT-type deposit, whereas the Fe-Mn ore can be classified as a stratiform-syn-sedimentary deposit. The formation of the MVT-type deposit is associated with a hydrothermal fluid system with a mean temperature of 183°C and mean salinity of 12.85 wt. % NaCl equivalent. The syn-sedimentary Fe-Mn ore, which is largely associated with calc-silicate lithologies, consists mainly of magnetite and hematite with minor pyrite, hausmannite and jacobsite, and was deposited by diagenetic and mixed diagenetic-hydrogenetic processes under changing oxic and anoxic conditions within the sedimentary basin. Acceptable geochemical exploration indicators of the existing mineralization include anomalous values above 0.5% Cu, 0.2% S;0.05% Pb;0.04% As;0.01% Zn;V, W, Mo, and Ag are 0.002%. Mineralogical indicators include chalcopyrite, bornite, covellite and galena with minor chalcocite, sphalerite, and tennantite for the Cu-Pb MVT-type ores at Kombat Mine.

A continental back-arc setting for the Namaqua belt:Evidence from the Kakamas Domain

A study of the NW Kakamas Domain in South Africa/Namibia provides a new,unified lithostratigraphy and evolutionary history applicable to the whole Namaqua Sector.The Mesoproterozoic history ranges from~1350 Ma to 960 Ma,but isotopic evidence suggests it was built upon pre-existing Paleoproterozoic continental crust that extended west from the Archaean Craton.In eastern Namaqualand,early rift-related magmatism and sedimentation at~1350 Ma occurred in a confined ocean basin.Subsequent tectonic reversal and subduction at~1290–1240 Ma led to establishment of the Areachap,Konkiep and Kaaien Domains.In the Kakamas Domain,widespread deposition of pelitic sediments occurred at~1220 Ma(Narries Group).These contain detrital zircons derived from proximal crust with ages between~2020 Ma and 1800 Ma(western Palaeoproterozoic domains)and 1350–1240 Ma(eastern early Namaqua domains),suggesting pre-sedimentation juxtaposition.The pelites underwent granulite grade metamorphism at~1210 Ma(peak conditions:4.5–6 kbar and 770–850°C),associated with voluminous,predominantly S-type granitoid orthogneisses between~1210 Ma and 1190 Ma(Eendoorn and Ham River Suites)and low-angle ductile(D_(2))deformation which continued until~1110 Ma,interspersed with periods of sedimentation.This enduring P-T regime is inconsistent with the expected crustal over-thickening associated with the generally-accepted collision-accretion Namaqualand model.Rather,we propose the Namaqua Sector is a‘hot orogen’developed in a wide continental back-arc with subduction west of the present-day outcrop.The observed high geotherm resulted from thinned back-arc lithosphere accompanied by an influx of mantle-derived melts.Ductile D_(2)deformation resulted from"bottom-driven"tectonics and viscous drag within the crust by convective flow in the underlying asthenospheric mantle.This extended tectonothermal regime ceased at~1110 Ma when SW-directed thrusting stacked the Namaqua Domains into their current positions,constrained in the Kakamas Domain by late-to post-tectonic I-type granitoids intruded between~1125 Ma and 1100 Ma(Komsberg Suite).The thermal peak then shifted west to the Bushmanland and Aus Domains,where voluminous granites(1080–1025 Ma)were associated with high-T/low-P granulite facies thermal metamorphism and mega-scale open folding(D_(3)).Unroofing of the Namaqua Sector is marked by large-scale,NW-trending,sub-vertical transcurrent dextral shear zones and associated pegmatites and leucogranites at~990 Ma.