Mutamba - Jangamo, Dongane, Ravene


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The Mutamba heavy mineral sand deposit collectively is made up of three significant mineralised zones, Jangamo, Dongane and Ravene, located ~40 km south of the town of Inhambane, Inhambane Province, Mozambique and are ~470 km by road northeast of Maputo along the coast.
(#Location: 24° 13' 52"S, 35° 21' 51"E).

The deposit occupies a stretch of Indian Ocean coastline ~45 km long by 10 km wide, which forms the southern end of the Inhambane Peninsula.

The coastal region of southern Mozambique forms part of the Mozambique basin, which is up to 400 km wide, with an onshore area of about 270 000 km2 and a long axis of about 1200 km (Förster 1975; Matthews et al., 2001). It is characterised by a complex sequence of Cretaceous to Quaternary age sedimentary rocks and unconsolidated sand deposits which rest unconformably on Karoo Supergroup sedimentary and volcanic rocks (Salman and Abdula 1995; Schlüter 2008; Emmel et al., 2011). The base of the post-Karoo sedimentary sequence comprises a very thick continental sediment known as the Red Beds Formation (Cilek 1989; Mashaba and Altermann 2015). The Red Beds are overlain by glauconitic sandstones and arenaceous limestones of the Maputo Formation, defining a transition to marine conditions during the Neocomian (Salman and Abdula 1995). The remainder of the Cretaceous is represented by a variety of rock types that are of marine, continental and transitional origin, suggesting tectonic activity caused differential uplift (Förster 1975; Salazar et al., 2013 Salazar).

The bulk of the overlying Caenozoic succession is a shallow-marine facies typical of a passive continental margin (Salman and Abdula 1995; Rutten et al., 2008), made up of two sedimentary cycles separated by an unconformity. These comprise a Palaeocene to Eocene cycle of glauconitic sand, clays and marls, and an Oligocene to Neogene cycle, that comprises terrigenous deposits of the Limpopo River and Zambezi River deltas. The interval between the Limpopo and Zambezi Rivers remained a shallow-water environment during the Neogens and comprises the Inharrime, Temane and Jofane Formations (Salman and Abdula 1995). An extensive regression at the end of the Pliocene to early Pleistocene produced a widespread set of coast-parallel dunes, alluvial river terraces and lacustrine deposits, gradually progressing seaward (Förster 1975; Wright 1998).

The current coastal plain is an extensive low-lying zone of unconsolidated Quaternary to Recent sediments (Palalane et al., 2015), separated from the Ocean by both older stable palaeodunes and active dunes. The cordon of active dunes are up to 2 km wide, and in many places >100 m above sea level (Momade and Achimo 2004). Modern beach rock is intermittently exposed along the exposed high-energy wind and wave-dominated shore (Armitage et al., 2006; Peché 2012), commonly comprising cemented calcareous sandstone (Cilek, 1985). Wright (1998 Wright, I. 1998. Coastal erosion processes in conjunction with rapid Quaternary sea level change in Mozambique, caused unconsolidated coastal sediments to undergo numerous cycles of erosion, transport and deposition, which allow winnowing of enriched secondary sources of more resistant minerals, including rutile, ilmenite and zircon, into localised HM placer deposits.

The bulk of the titanium and zircon sand mineralisation are associated with at least 160 m of older marine-intertidal-aeolian sediments that include three generations of the stable older palaeodunes (D1, D2 and D3) which occur inland of the coastline and overlie a package of marine-intertidal sediments. Unit D3 is the most important in terms of economic geology, with an average of 3.3% Total HM and low slime content, making it potentially amenable to low-cost dredge mining methods. These are overlain by the contemporary aeolian D4 unit and alluvial material.

D1 is the oldest aeolian deposit overlying the Intertidal unit, and is composed of a dark red to red-brown silt-rich (>20%) palaeodunal quartz sand, with an average THM of 1.3%, although its high slime content precludes it from being considered part of the mineralised envelope. In the Jangamo zone, D1 forms a core onto which subsequent aeolian sands were deposited and is associated with some of the highest elevation in the area. Most of unit D1 is completely obscured by a variety of younger sediments.

D2 is the most common unit overlying D1, and comprises is light to dark orange-brown quartz sand with an average slime content of 8%. The contact between D1 and D2 is mostly defined by a distinct drop in the slime content from about 18 to 20% to 8% respectively. Sediment interpreted to represent D2 palaeodunes has an average of 2.8% THM and is an economically important unit.

D3 overlies D2 and comprises a generally looser and more free-flowing quartz sand sequence, that occurs in a long, low series of parabolic landforms with NW-SE axes, interpreted as aeolian sediments. The D2 to D3 contact is best defined by the slime characteristics, with the latter averaging about 6.3%.

D4 is mainly composed of yellow-white and grey free-flowing quartz sand which overlies D3, and represents the modern frontal dune system adjacent to the contemporary coastline. These modern frontal dunes are till mobile with extensive areas of exposed, unvegetated sand with an average grade of 2.7% THM.

The better heavy sand mineralisation at Mutamba has occurs within the three main zones of Jangamo, Dongane and Ravene, all of which have relatively similar mineralisation characteristics. The combined ilmenite, rutile and zircon economic HM content is 60 to 80% THM, with the bulk of the mineralisation hosted by the D2, D3 and Fluvial units. The THM grain-size distribution for Mutamba has a range 90 to 210 µm, with 50% of HM grains >142 µm. The overall slime content for Mutamba is 7.1% and typically comprises kaolinite and illite, with lesser amounts of smectite, chlorite and mica.

The Mutamba and similar sized Chilubane deposit, some 150 km along the coat to the WSW, have a reported globally significant 'Exploration Target' of 7 to 12 Gt of mineralised sand @ 3 to 4.5% THM, comprising >140 Mt of ilmenite and 10 to 15 Mt of contained rutile + zircon (Dumouchel, Hees and Alvin, 2016).

The most recent source geological information used to prepare this summary was dated: 2016.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.


  References & Additional Information
 References to this deposit in the PGC Literature Collection:
Dumouchel, J., Hees, F. and Alvin, M.P.,  2016 - Coastal evolution and associated titanium sand mineralisation of Jangamo district, Inhambane Province, Mozambique: in    Trans. IMM (incorp. AusIMM Proc.), Section B, Appl. Earth Sc.   v.125, pp. 140-152.

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