re: Ann: High Grade Outcropping Base Metals D...
the way i see it i can see three waves of news
kaskara
kaskara is the first of the exploration sites on tsumeb type mineralisation, with the current threshold being about 200 meters in terms of maximum drilling reach on the lower section of the kaskara hill
the road is being constructed, so it will eventually make its way to the top of the kaskara hill and the larger drill rig will have access to the regions we all want the rig to be
right now i think they will be drilling the lower reaches of the foot of the hill until the road is completed
my understanding is that the absolute desire is to drill from the top of the hill and further south and follow the main seam down. everything being seen in the drilling ths far replicates all the regions where very large discoveries have been made.. tsumeb was some 900 meters deep i believe, and i believe some 300 meters long, this kaskara structure is thought to be 900 meters long and thus far, only been drilled to about 200 meters, with heavy mineralised regions being encountered and no end to it!! i have a strong feeling this rig, that is capable of far deeper reaches, will get to discover the deeper sulphide regions..
what they are seeing is a classic text book tsumeb type structure.. this is no Mississippi valley play like border
Structural evolution of the Otavi Mountain Land, Namibia
The Otavi Mountain Land (OML) in Northern Namibia is located in the Northern Platform Zone of the eastnortheast striking intracontinental branch of the Damara Belt, at the southern margin of the Congo craton. The lithologies in the OML are mainly shallow water carbonates and siliciclastic rocks of the Neoproterozoic Damaran Supergroup. The structural evolution of this part of the Damaran Orogen is still unclear, although economically important base metal deposits in the OML are structurally related. Tsumeb-type and Berg Aukas-type deposits are associated with flexural shear folds and small-scale thrusts and indicate the importance of brittle shear zones for the formation of mineralization (Pirajno & Joubert 1997).
Types and stratigraphic setting of mineralizations
The ore deposits in the OML can be grouped into different types. Due to the ongoing research, this is of course only a preliminary classification:
Askevold-type low grade Cu-Ag-Au associated with volcanics and emplaced in dolomites and diamictites, Nosib-type Cu-Pb mineralization along Nosib Group � Abenab Subgroup contact, Berg Aukas-type Zn-Pb stratabound deposits in carbonate rocks, Tsumeb-type Pb-Cu-Zn pipe-like deposits in carbonate rocks, Tschudi-type low-grade Cu mineralization in sandstones and conglomerates at the base of the Mulden Group, Abenab-type Vanadium deposits in post-Damaran karst pipes and breccias, Sand-sack type Vanadium deposits in younger karst-and-caliche sediments.
Type 1 is present in diamictites of the Chuos Fm. and in the dolomites of the overlying Abenab Subgroup. This small low grade Cu-Ag-Au mineralization might be a VMS-type deposit.
Type 2 occurs at the tectonized contact between clastics of the Nabis Fm. and laminated dolostones of the overlying Abenab Subgroup. It is characterized by small deposits with high grade secondary Cu-Pb mineralization.
Type 3 comprise many small to medium-size deposits, mostly hosted in the Abenab subgroup. It is thought to be similar to many other Mississippi Valley-type mineralizations in the world: late diagenetic and related to a pre-Damaran fluid flow involving basinal brines. At Berg Aukas and Abenab West large tonnages of non-sulfide Zn-ores (willemite & smithsonite) occur.
Type 4 comprises not so many deposits, but mostly of larger dimensions and tonnage than those of type 3. The main characteristics of the best-known deposits (Tsumeb & Kombat) hosted in the Tsumeb Subgroup are the high Cu content, the presence of different breccia types and the zoned pipe structure. Both types 3 and 4 show a clear structural control.
Type 5 comprises only the Tschudi mine with its Cu-Ag mineralization, oxidated to more than 80 m in depth, impregnating the clastic sediments of the Mulden Group.
Type 6 is mostly present in the Abenab pipe, but also locally in the Berg Aukas mine and in other smaller occurrences.
Type 7 is mostly diffused as relatively surficial concentrations in karst deposits and in caliche sediments and crusts from Tertiary to Recent. Both deposit types 6 and 7 are thought to be of supergene origin.
Ore deposits of the Otavi Valley (southern OML)
In the cross section through the Otavi Valley isoclinal folded and thrusted formations in the south and open folding in the north are shown. In the centre of the Otavi Valley is the tectonic (syn-Damaran) contact of the Tsumeb Subgroup and the Mulden Phyllites. Along this contact drag folds and piercement structures of the phyllite into the dolomites occur. In the southern Otavi Valley the phyllite is "squeezed out" to the north.
Another prominent feature in the centre of the Otavi Valley are large strike slip faults, which might extend into graben structures of the basement.
Sketch of a cross section through the Otavi Valley in the area of Kombat and Gross Otavi (southern OML).
Kombat roll structure
The main mineralization at Kombat is of the Tsumeb type, but even heavilier deformed. One difference to the Tsumeb pipe lies in the impregnated drag folds or roll structures. A remobilization of the primary Pb-Zn-sulphides in the brecciated horizons into the core of the roll structure might happen during the main Damaran orogenic phase. The overthrusted sorrounding phyllites could have acted as a dam for the ascending metall-rich fluids.
Cu-Fe-sulphide mineralization at Kombat (southern OML).
Gross Otavi
In Gross Otavi two different types of mineralization are recorded. At first primary hypogene Pb-Zn-sulphides in a sollution collapse breccia in the upper Tsumeb Subgroup. This deposit belongs to the Berg Aukas type. Second miocene karst fillings with supergene disseminated V-mineralization are preserved.
Sketch of a cross section through the Gross Otavi deposit (southern OML).
Solution collapse breccia at Gross Otavi (southern OML).
Coward, M.P. (1981): The junction between Pan African mobile belts in Namibia: its structural history.- Tectonophysics 76: 59-73.
Frimmel, H.E., J.G. Deane & Chadwick, P.J. (1996): Pan-African tectonism and the genesis of basemetal sulfide deposits in the northern foreland of the Damara Orogen, Namibia.- Spec. Publ. � Society of Economic Geologists, 4: 204-217
Pirajno, F., Joubert, B.D. (1997): An overview of carbonate-hosted mineral deposits in the Otavimountain land, Namibia, implications for ore genesis.- Journal of African Earth Sciences 16 (3): 265-272.
Raab, M.J., Brown, R.W., Gallagher, K., Carter, A., Weber, K. (2002): Late Creaceous reactivation of major crustal shear zones in northern Namibia: constraints from apatite fission track analysis: Tectonophysics 349: 75-92.
(20min delay)