The Dodoma Morogoro Handeni-Magambazi Area, Eastern Tanzania —A Proterozoic Sediment Hosted Vein Deposit

Abstract

The Handeni area on the eastern edge of the Tanzanian Craton is within the Neoproterozoic Pan African Orogeny Mozambique Belt has been considered the area to be part of the “Sumukuland Corridor”. In this paper, it is postulated to be Sediment Hosted Vein Deposits. Tanzania is the third-largest gold producer in Africa with an annual production at 60 tonnes. The Archaean Tanzanian Craton is surrounding Proterozoic Usagaran and Ubendian mobile belts. Outside of the Craton in the Ubendian only one mine is operating, to the southwest and one deposit in the “Kilindi Handeni Superterrane” to the east. The Pan-African Mozambique Metamorphic Belt to the east stretches from the south of Mozambique to Sudan and Ethiopia contain significant amount of gold in the Handeni-Morogoro-Dodoma area. The high metamorphic terrane between Morogoro and Handeni, has “cooked” the original rocks so identifying their origins is tenuous, but has copious amounts of garnets associated with regional metamorphism of sediments and volcanic. The Mozambique Metamorphic Belt represents one of the major sites of Gondwana amalgamation related to the Pan African Orogen, where two major orogenies are superimposed on each other. The Asian SHVs are at major Cratonic collisions part of the Central Asian Orogenic Belt with the Siberian Craton to the north and three Cratons to its south. This belt was the structural preparation of the Tien Shan Area with many deep sutures and thrusts for the deposition of the SHV deposits. These Cratonic collisions of the Asian Continent would be analagous to Gondwana’s “collision” of East and West Gondwana. Sediment-Hosted Vein deposits are the largest gold-bearing vein deposits, along paleoTethyan margins of central Asia. The key features of passive margin settings that control mineralization include: 1) an unstable substrate of extended continental crust (comparable to the Tanzanian Craton); 2) a thick sedimentary sequence with associated syn- to post-depositional extension and contraction structures; and 3) reactivation and interplay between these components during fold-thrust deformation to provide pathways for deep-sourced hydrothermal fluids and magma. This south Siberian Craton (SSC) region has deposits and mineralization related to hydrothermal breccias and veins into the Paleozoic sediments as definitive models of SHV deposits. Major “sutures” are present. The Usagaran and Ubendian formations could be in an analogous tectonic zone. In the SSC region, the Central Asian Orogenic belt has identified oceanic assemblages, analogous to the opening and closing of the Mozambique Ocean similar assemblages, southeast and east of the Tanzanian Craton, as opposed to being reworked Archaeon Sumukuland Corridor. The Muruntau gold deposit is situated in Uzbekistan, have several structures, controlling the localization of the ore bodies in metasedimentary units, related to the bedding and schistosity, located sub-parallel to flat-dipping zones of thrust, shear and mylonitization and controlled by brittle deformation behavior of the rocks after metamorphism (not discordant with the Pan African Orogeny). SHV deposits have placer gold deposits and in the Handeni Morogoro area many placer have been found by the locals including the Magambazi deposit. Instead of the overprinting of the Archaean terrane, an accreting sequences of oceanic volcanics and sediments during the closure of the Mozambique Ocean with the formation of Gondwana being subsequently metamorphosed and “thrust” faulted against the Tanzanian Craton with the introduction of “fluid granitic magmas” is suggested. Island arcs are extremely prolific in mineralization. The “Mozambique Ocean” amphibolites as island arc remnants would be natural hosts and structurally “available” to enable mineralization in the Pan African Orogeny. There are oceanic assemblages in the Tien [Tian} Shan Accretionary Belt with less metamorphic intensity. The alternate Sediment Hosted Vein model, is proposed for the Kilindi Handeni Superterrane hydrothermal Orogenic gold deposits with metamorphism and deposition of gold along the continental collision structures. The parameters for a SHV deposit are present in the Handeni area. An “older” North American example of this level of metamorphism, associated with continental “accretion and/or collision” is the Adirondacks and the Grenville geologic province. Comparing the SHV and Archaean Overprint model, for the Orogenic gold mineralization, the SHV model fits.