The pegmatite field in the area is situated in a border zone between two tectonic domains. To the north is an area dominated by unfoliated or weakly foliated granites in which the foliation shows no consistent orientation. To the south the country rocks are comprised of gneisses and schists in which a penetrative, generally E-W foliation is developed. These two domains were termed the Richtersveld Subprovince and Bushmanland Subprovince
The granites of the Richtersveld Subprovince comprise an intrusive suite, the Vioolsdrif Suite, of batholithic nature and were dated at approximately 1,900 Ma for the mafic members, to approximately 1,730 Ma for the felsic members (e.g. Reid, 1977). They are intrusive into a succession dominated by volcanic rock types and also containing subordinate sediments dated at approximately 2,000 Ma and which are, based on isotope studies, related to the same magmatic event (Reid, 1977). This volcano-sedimentary succession (Orange River Group) occurs as remnants on various scales in the granites and according to Blignault (1977), a synclinal structure related to pre-intrusion deformation can be recognized in the unit to the east of Vioolsdrif.
In the Bushmanland Subprovince the intrusive gneisses (granodioritic) intrude into schists and gneisses, some of which the protoliths are controversial but a large proportion of which are clearly metasedimentary (such as the biotite schist) . Geochronological ages of 1,200 Ma (e.g. Joubert, 1986) are accepted to represent the metamorphic age related to the peak of deformation in this subprovince.
The pegmatites in the licence area are mainly developed in granodiorite of the Vioolsdrif Suite. A large proportion is also developed in the leucocratic alkaligranites of the suite, however, all the studied pegmatites are situated in the granodiorite and most of the pegmatites in the leucogranite seem to be barren.
Hugo (1970) concluded that there are two phases of pegmatite intrusion in the pegmatite belt of the Northern Cape, viz. an older phase at 1,000 Ma associated with the closing stages of the Namaqua orogeny, and a slightly younger phase at 950 Ma related to the intrusion of isolated bodies of late- to post-tectonic granitoids.
Application accepted and granted by the DME.
Located north of the O’kiep copper field that covers an area of approximately 3 000 km2.
Located in the Pofadder pegmatites fields
Potential for Cu, Li, Be, Ta, W and REE
Limestone- Kinderle Limestone Project
Uranium anomalies (grade upto 6.2kg/t)
Types of Pegmatites
Pegmatites have been classified by Ginsburg et al. (1979) according to their depth of formation, mineralization, and their relationship to igneous processes and metamorphic environment:
- Miarolitic pegmatites. These are generally intrusive into low-grade metamorphic rocks and often contain cavities bearing optical fluorite, gem quality beryl, and topaz. They are found within, or in close proximity to, granites, and their direct relationship is unquestionable. Where they intrude the country rocks, they extend for only limited distances.
- Rare-element pegmatites. These are enriched in granophile elements (Li, Rb, Cs, Be, Ta, Nb and minor Sn) and often fill fractures in cordierite-amphibolite facies rocks. They are generated from differentiated granites which, in general, have been transported. These pegmatites are often associated with granites which have been intruded into tectonically active regimes along deep fault systems (Cerny, 1982a). Granites that generate rare-element pegmatites of intermediate depth tend to be late- to post-tectonic granites of calc-alkaline affinity which have been emplaced along previously formed faults and fracture systems during the waning stages of tectonic activity. These granites are typically leucocratic, biotite-bearing, two-mica, or muscovite-bearing granites and contain accessory garnet, tourmaline, cordierite and/or andalusite.
- Mica-bearing pegmatites. These are usually hosted by upper amphibolite facies metamorphic rocks and commonly carry extensive mica reserves and minor, if any, rare-earth elements. They are products of anatexis (partial melting) or are separated from anatectic, more or less in place or autochthonous (S-type) granites.
- Abyssal. These pegmatites are generated in granulite facies terrains and are usually barren, though locally they may contain allanite, monazite and corundum. Furthermore, these pegmatites often grade into migmatites and display no direct relationship with granitic bodies. They are usually conformable to the host rocks.
Mining of Pegmatites
The sporadic nature of mining activities on these pegmatites has been caused by a variety of factors. The most important ones are:
- The mineral or minerals which are in demand at the given point in time.
- Highly variable commodity prices over time.
- The decision between domestic and export markets.
- The influence of transport costs – the largest single contributor to operational costs.
- The unpredictability of the yield for the accessory minerals (caused by the nugget manner in which they are distributed in the ore body), some of which are currently fetching high prices on the international markets, and did so historically.
- The low yield due to inefficient small scale mining methods.