Introduction.
Higher gold prices inevitably stimulate interest in potential gold mineralized areas, particularly in marginally profitable gold deposits or even terranes or regions where the model for potential gold mineralization is poorly understood. One such geological terrane is the southern regions of the Western Cape Province and the southwestern regions of the Eastern Cape where historic gold mines and gold showings are documented. Rock units involved in this discussion include the Malmesbury Group, The Kaaimans Group, The Cape Granite Suite, The Cape Supergroup and the Karoo Supergroup.
In this communication, the theoretical background to gold mineralization in the rock types mentioned in the first paragraph is discussed. Specific localities, maps and place names are not provided in order to avoid creating high expectations among interested but poorly informed opportunistic parties as so often happens. Where reference is made to findings of previous works, references will be provided to interested parties with a track record in gold exploration. SearchMinSA will gladly evaluate the credentials of the interested individual, company or group and enter into discussions on the topic.
The aim of the communication is to stimulate discussion and research on gold mineralization in the Western Cape Province.
Gold Showings and historic mines in the Western Cape Province.
Gold Mineralization related to pre-Cape Rocks.
Gold showings in the Malmesbury Group.
The best described gold enrichment in the Malmesbury Group is an occurrence in which gold is enriched during an early deformation event (D1). It is suggested (1) that the gold is related to an early D1 deformation event predating the intrusion of the CGS (Cape Granite Suite). The fluids are presumed to be the result of devolatilization of metamorphic rocks during lower greenschist metamorphic conditions, most likely sourced from the hydrous sedimentary pile of the lower units of the “Swartland Group” (1).
Although the gold has been described as “invisible” (1), sampling of stream sediment samples and panning of the area (personal exp. 1994 and an exploration company (2)), yielded visible gold grains. In the broader context of gold mineralization in the Western Cape, this style of mineralization is of importance as it illustrates the presence of low level gold in the metasediments of the “Swartland Group” and the mobilization of the gold under low grade metamorphic conditions, described as mesothermal gold mineralization. As this event is interpreted to illustrate concentration of gold prior to the intrusion of the CGS, remobilization of this gold would potentially be possible during and following the intrusion of the CGS as well as during subsequent geological events potentially re-concentrating gold already accumulated during the D1 event. Data to date seems to illustrate that the D1 event on its own only concentrated gold to sub-economic values.
Gold potential of the Kaaimans Group.
Multiple episodes of metamorphism, deformation and granitic intrusion characterize the pre-Cape Kaaimans Group. Of particular interest to gold mineralization is the last phase of retrogressional deformation and associated fluid flow following three periods of compression, affecting both pre-Cape and Cape Supergroup rocks. A spread in intrusion age of granitic rocks from early deformation to late stage deformation and possibly post deformation is suggestive of an extensive period of fluid flow and potential trap site creation associated with these granites and their surroundings. The presence of skarns in the Kaaimans Group is also of note.
Work conducted during 1976 and 1977 ((3) and (4)) argues that the intrusion of the Maalgaten granite and Rooiklip granite gneiss took place during and/or just prior to early deformation (F1) of the Kaaimans Group as the foliation S1 and lineation L1 are recognized in both the metasediments and the granites. The granites supplied heat to the country rock prior to and during the deformation event. The Maalgaten and Rooiklip granite gneiss were evidently affected by the F1 deformation event. This differs from the early deformation events recognized in the Malmesbury Group (D1) pre-dating granite intrusion. The F1 event in the Kaaimans Group is considered to be part of a regional metamorphic event during which at least part of the heat was supplied by granite intrusion and cooling. Mineral assemblages during the F1 event suggest metamorphic conditions reaching lower amphibolite grade (5), which would be higher than metamorphism for the Malmesbury Group. The F2 event in the Kaaimans Group seems to be medium grade (upper greenschist?) conditions followed by a retrograde F3 event (lower greenschist) synchronous with the deformation of the overlying Cape Supergroup sediments, evidently at a much later stage. Work published in 1980 (5) ascribed the presence of chlorite, opaque minerals and muscovite in the metasediments along glide planes in the metasediments and mylonites in the granites, to the F3 event. This deformation event promoted the distribution of water and volatiles in the Cape Supergroup, the contact zone between the Cape Supergroup and the pre-Cape rocks as well as in the pre-Cape metasediments and igneous rocks. It should be noted that the Bokkeveld Group is also affected by greenschist facies metamorphism.
Preserved magnetic fabric (AMS) work (6) seems to illustrate that the Saldanian deformation event and the Cape orogeny deformation event are distinctly separate and that the Cape Orogeny did not affect the pre Cape rocks to a large extent. The latter conclusion is debatable.
The Rooiklip 2 granite as well as the Modderkloof granodiorite seems to be intrusive during the end of the F2 metamorphic event as they display none of the deformational features of the other Kaaimans Group related granites. These granitoids thus supplied a later heat flow events to the Kaaimans Group.
Gold related to S-type granitic intrusion.
Gold on the contacts of Sa1 granite and Malmesbury Group rocks.
In terms of reported gold grades, the gold occurrences in the Cape Town area ranks as of significance. Gold were mined in quartz veins on the contact of the Sa1 (10) Peninsula Granite and Malmsbury Group hornfels, average values reported to be 24.5 ppm (7), which represents substantial gold enrichment values.
The model for this style of gold mineralization in the Western Cape Province is poorly understood. Some aspects of importance are:
- Recent work (11) suggests that the depth of intrusion of these peraluminous granites are significantly shallower than previously understood and may be lower than 3 km, even as low as 2 km below surface. Fluid phase seperation and mixing of magmatic and meteoric fluids may become an important aspect under these conditions, transporting gold to higher levels and deposition of the element in suitable mechanical and geochemical trap sites.
- The host rock to granite intrusion, the Malmesbury Group, is highly diverse and includes volcanic and sedimentary sequences in the depositional pile. Enrichment of gold associated with the volcanic sequence within the Malmesbury Group prior to remobilization during Sa1 granite intrusion is most likely a contributing factor as described above.
- A combination of lithology, chemical gradient as well as structural trap sites due to folding, thrusting and faulting in the Malmesbury Group undoubtedly played a role in the localization of gold enrichment on Sa1 granite-Malmesbury Group contacts.
- Under the proposed high levels of intrusion, the role of meteoric water in the vicinity of contact zones becomes an important factor in potentially remobilizing gold.
- The gold enrichment in these localities may also have benefitted by contribution of meteoric fluids from the Cape Supergroup sedimentary pile and deformation during the Cape orogeny.
From the above it is evident that more scientific work on the mechanism of these deposits related to Sa1 intrusions will undoubtedly reveal a prolonged and complex origin for gold deposition. As a first step the possibility that Sa2 granites as described below, may be involved needs to be investigated.
Gold related to Sa2 type granites.
Gold associated with Sn deposits.
Exo- and endo granitic Sn occurrences are well known in the greater Cape Town area, some of the deposits have been mined in the past (7). Sn is present as cassiterite with W present as wolframite. The hydrothermal fluids associated with the Sn deposits are generally closely related to Sa2-type granites of the Cape granite suite. Gold (Au) occur in minor concentrations in these deposits, mostly where pyrite and arsenopyrite is present in lodes proximal to contact zones. Fluid inclusion investigations revealed the presence of minor amounts of gold in the Sn lodes associated with high level hydrothermal brecciation and Na (B) (boron) metasomatism of the granite.
Although Sn, As and Au deposition is generally located in close approximation to granitic intrusions, mineralization is, in rare occasions, related to structural trap sites in the Malmesbury Group (12).
In summary it may be stated that Sn, As and Au deposition is related to Sa2 granite intrusion, mineralization is found in hydrothermal zones related to granite intrusion or within granites with a Sa2-type affiliation. The S-type granites with the highest potential for Au associated with Sn deposits fall within the Sa2 type of (10) and (13). They are characteristically Na (B) – metasomatised as indicated by the presence of tourmaline nodules (12). These granites are also typically P – enriched (14). Although some “greisen-type” Sn and W – mineralization has been described associated with some of these intrusions, gold enrichment in the Sn-W quartz veins could not be verified.
Gold related to Sa2-type granites with cataclastic deformation.
Elevated gold contents are often encountered associated with the Sa2 granites ((10) and (13)). As described above, these granites show signs of Na (B) – metasomatism and in the case of Sn – Au associations of high level, even subvolcanic intrusion.
Some Sa2 granites with elevated gold content without apparent Sn mineralization are encountered. Although the trace element composition shows enrichment in Sn and W, the most important feature in terms of gold mineralization is the fact that the granite has been cataclastically deformed, most likely during the Cape orogeny (15). Gold re? -mobilization seems to be related to this much later overprinting event.
Gold related to I – type CGS granitic intrusion.
Ia Plutons.
To provide background to readers not familiar with the Cape Granite Suite (CGS), some of the characteristics of plutons related to Ia type (CGS) are briefly discussed:
The I-type granitoids of the CGS show a number of general features which are typical of late to post collisional granites (Caledonian I-type granites) such as the Scottish Highlands granites) (16). Some of these features are:
1) minor diorite and gabbro in association with large volumes of felsic rocks, 2) biotite as the dominant mafic mineral, 3) dispersed, isolated plutons surrounded by strongly discordant contact metamorphic aureoles and 4) lack of important dyke swarms.
Geochemical data indicate that the CGS I-type associations are plutonic equivalents of late orogenic high-K calc-alkaline volcanics (18). They are metaluminous to weakly peraluminous (molar Al2O3 / (K2O+Na2O+CaO < 1.1, molar K2O / Na2O < 1 and normative corundum < 1), characteristic of typical I-type granitoids. Fe2O3 / FeO ratios vary from 0.5 to 0.8 suggesting a magnetite series granitoid affinity (17) and confirmed by an abundance of magnetite in the majority of the I-type plutons (18).
Phase II (I-type) granites of the CGS may be related to shoshonitic or high potassium calcalkaline volcanism and are typical of magmatism in island arcs or active continental margins (18). High potassium calcalkaline associations are generally explained by some crustal contamination of a mantle derived alkaline magma (19) or differentiation from initially contaminated alkaline magma (20). Recent work on the Yzerfontein outcrops (21) confirmed the shoshonitic nature of these rocks, considered to be the “smoking gun” in terms of the description of the origin of CGS mafic to intermediate rocks. The “smoking gun” (21) is the confirmed conclusion that high potassium calcalkaline (even shoshonitic) mantle derived mafic magma provided the heat source for the melting of crustal material (interpreted to be the Malmesbury Group) to produce the CGS. In terms of source material there is also strong evidence for a significant contribution of Namaqua – Natal belt remelting (18), either direct or from material deposited in the Malmesbury Group sourced from the Namaqua – Natal belt rocks. Various recent studies seem to suggest this.
An important criterium in terms of mineralization potential of I type granites of the CGS is the P/Ca ratio which is low for granites with W-Mo skarn related mineralization potential and high for the unmineralized types. The presence of calcareous or dolomitic wall rocks is commonly associated with the formation of these mineralized skarns. The Ia granites with the above favourable ratio are associated with endo- and exo-skarns with mineralization consisting mainly of scheelite and molybdenite. Gold and arsenopyrite may occur in veins or hydrothermally altered shear zones within or distally to this particular granite phase.
Examples of Ia CGS rocks with gold mineralization related to the Ia granitoids are:
Mafic and intermediate plutonism (gabbroic to dioritic).
Two events of mafic to intermediate plutonism in the southwestern Saldania mobile belt are related to phase I (to be confirmed by dating) and phase III of the granitoid plutonism respectively. Those plutons related to phase I are intrusive in the Swartland terrane (Malmesbury batholith) and are composed of olivine gabbro, gabbro norite, gabbro, diorite and granodiorite (chemical classification). The plutons related to phase III are intrusive in the Tygerberg terrane and the rock types are olivine gabbro, gabbro, monzogabbro, monzodiorite, syenodiorite, monzonite, granodiorite and quartz syentite (chemical classification). Intrusive relationships indicate that the gabbroic components preceded intrusion of the other phases. A U-Pb isotope dilution thermal ionisation mass spectrometry (ID-TIMS) composite zircon age of 519 ± 7 Ma have been reported (22, 23), whereas an average U-Pb zircon crystallisation age of 535 ± 3 Ma suggests a closer temporal association with the ~545 to 535 Ma S- and I-type granites of the CGS (24). These ages put this magmatism on the border of Phase II and Phase III as previously interpreted (13). Quartz monzonite as well as quartz syenite dyke swarms and aplitic pebble dykes containing enclaves ranging in composition from pyroxenite to quartz syenite are abundant in some of these plutons.
Minor enrichment of Au (and Cu) is observed in a series of late hydrothermal veining with gold grades varying between 0,4 g/t and 12 g/t (22, 23). Extensive fluid inclusion work (23) as well as application of chlorite geothermometry illustrated the complex nature of fluids related to these sulphide veins, in general crystallizing below 290°C. The fluids related to some plutons are more Ca-rich than others (the latter Na-dominant), but both contain a CO2 component. Isotope work (22) convincingly illustrated that the fluids responsible for the crystallization of these veins (with elevated Au) were related to a meteoric fluid dominant epithermal system at relatively low temperatures (170° – 300°C) and at low pressure (0,5 to 1,6 kb), essentially confirming the findings of ((23) and (22)). The lack of extensive mineralization is ascribed to the restricted mixing of meteoric and magmatic water (22). The presence of hydrothermal breccia dykes caused by an overpressure of CO2 (and H2O) may be important in the localization of Au (and Cu-Zn sulphides) mineralization in the Malmesbury Group above these mafic and especially intermediate Ia plutons. The brecciation event may have facilitated fluid mixing.
Intermediate plutonism (granodioritic).
Minor (in outcrop area) highly altered granodiorite with some Cu mineralization and traces of gold are found intrusive into the Malmesbury Group (7). Alteration of the rock most likely took place under epithermal conditions such as described above.
The Kaaimans Group Ib granites.
Type Ib granitoids with a favourable P/Ca ratio may also be associated with scheelite- and molybdenite -bearing endo and exo skarn-type mineralization. Their higher oxidation ratio than the Ia-type granites, however, also allows Sn-U-Au-exo-skarn formation. Some of these granites show anomalous U-Th concentrations and are anomously enriched in U, Sn and W. Distal phases of these plutons may be explored for skarn related gold.
Calcic skarns related to I-type plutons.
The Riviera pluton (well discussed in the public media) is a medium to fine grained equigranular metaluminous to peraluminous (Ia and Ib type) quartz monzonitic to granitic pluton with a possible late Aa intrusive event. W-Mo (Cu) (REE) mineralization is closely related to calcic exo- and endoskarn. Some elevated Au values are observed in exo- as well as endoskarn samples. W is in this case present in scheelite, differing from W mineralization in the Sa2 – type Cape Granites (W present as wolframite).
Magnesian skarns related to I-type plutons.
Endo- and exogranitic W mineralization (in scheelite) is also found within and proximal to magnesian Ia type plutons. Elevated Au values are encountered in exoskarn assemblages in the surrounding Malmesbury Group that is signficantly more magnesian than that of the calcic skarn relates I-type assemblages such as in the Riviera pluton.
I-type Intermediate to Felsic volcanism.
An extensive peraluminous volcanic phase (Postberg and Saldanha ignimbrites) related to the CGS is known. The existense of a metaluminous (I-type) volcanic phase related to the CGS is a realistic possibility. A hint of such volcanism was shown by the, apparently 533 Ma old, dacitic bolders collected (25). If such volcanism did exist, it is important in terms of Au mineralization.
Maitland Mineralization.
Vein and replacement style Cu-, Pb-, Ag-and Zn-sulphide mineralization at the Maitland mine near Port Elizabeth, is hosted by calcareous metasediments and could also be related to potentially nearby Ia granites.
Gold related to A-type Cape Granites.
The A-type granites of the CGS are chemically and mineralogically distinct from fractionated I-types as well as other highly fractionated granites of the suite such as the Sa2 granites (18). In terms of their gold mineralization the style of the mineralization event is also quite distinct. The felsic magmatism of this phase is subdivided into two A-type associations namely Aa and Ab. The granitoids of association Aa vary in composition from amphibole quartz syenite to biotite quartz syenite and alkali granite. Deformation is absent and highly scattered small (1 to 5cm) mafic enclaves are present. Metasedimentary enclaves are absent. Granites of the Aa association intruded in the Tygerberg terrane. The Ab association comprises mainly alkali feldspar granites and are intrusive in the Swartland terrane. The Ab granites show chemical characteristics very smilar to highly fractionated I-type granites of the CGS.
Although evidence for K and Na metasomatism is abundant in the Ab association granitoids, these granitoids are barren. They are enriched in the radioelements U and especially Th with high Th/U ratios. Desilicification and accompanying albitization with Th enrichment is a prominent feature of these plutons.
Hydrothermal breccia related Au mineralization.
The most significant Au mineralization is found within the Aa association. Cu-Mo (±Au) sulphides hosted by hydraulic breccia pipes, stocks and veins occurring in alkali feldspar granites and amphibole quartz syenites comprise the bulk of the mineralization in these plutons (26). The breccia bodies are small, approximately 75 m in diameter, and are the result of CO2 overpressure related to a major hydrothermal event. Breccia fragments are mainly from the granitic host rock but hypabyssal/rhyolitic enclaves indicate a high level of emplacement (<1 km) of the magma venting to the surface along fractures and breccia pipes. Ore minerals are auriferous arsenopyrite and molybdenite, with accessory pyrite, chalcopyrite and fluorite. It is important to note that to date, only the bottoms (root zones) of these breccia pipes have been encountered. This may imply:
a) Top parts may still be found in grabens.
b) The eroded tops may have led to a concentration of gold in sediments derived from the weathering of the CGS.
Gold related to the Cape- and Karoo Supergroups
Primary gold in quartz veins hosted in sandstone of the Table Mountain Group of the Cape Supergroup has been reported (7). In these rocks 127 kg of gold (approximately R136 million at current prices and exchange rates) was mined between 1887 and 1905 (only includes declared gold figures). Other estimates ((8) and (9)) reported total gold mined in these settings at between 80 kg and 112 kg. In some instances gold occurs along a strike distance of approximately 40 km in an E-W direction, including panned gold sites and hard rock workings.
The faulting, folding, shearing and thrusting associated with the deformation of the Cape Supergroup provided ample conditions for the entrapment of fluids in, mainly, tensional trap sites. Fluid inclusions were used (27) to illustrate that fluids associated with the lower Table Mountain Group indicate lower greenschist facies trapping conditions (240° – 300°C) as well as concluding that temperatures above 300° were reached during subsequent plastic deformation events. It was further concluded that this event pre-dated the thermal peak of the Cape Orogeny by 60 Ma, illustrating potentially relatively high temperature (lower to medium greenschist facies metamorphism) and H2O – NaCl – CO2 – CH4 fluid flow over an extended period of time. These conditions are favourable for the transport and deposition of gold in suitable trap sites.
The effect of the Cape Supergroup orogeny on the deformation of the pre-Cape rocks (see above) is a fact, the extent of which is somewhat controversial. The contact zone between the pre-Cape rocks and the Kaaimans inlier in the George – Knysna area is characterized by a high strain zone a few tens of metres in width with numerous quartz – filled tension gashes, mylonites and asymmetric folded quartz veins (28). The effect of the Cape Orogeny overprint on the underlying pre-Cape rocks in this region apparently disappears over short distances away from the contact zone. It is however evident that this contact zone represents an area of potential fluid migration, chemical gradients and likely deposition of metals including gold.
A long history of tectonic activity and reactivation of pre-existing fault structures played a critical role in the gold mineralization (29). The Cape Fold Belt provides the framework for structural traps to develop wheras extensional Mesozoic fault movements may reactivate earlier fault structures and provide conduits for mineralising fluids. The Kaaimans Group is proposed as the possible source for the gold (29). A potential heat source ascribed to Jurassic or Cretaceous igneous activity or a deep seated magma chamber has also been suggested (29). Fluid inclusion homogenization temperatures and salinities are in the range of typical Carlin-type sediment hosted Au deposit as proposed (29).
An important aspect mentioned by previous authors (29) is the possible influence of a “basement antiform” and the proximity of major faults as a key to the gold mineralization.
The hydrothermal Au in the Witwatersberg Goldfield is ascribed to have dominantly structural control (30). The Au associated quartz veins are localized along bedding planes, fold axes and a variety of semi-ductile to brittle faults. The deposits of the Witwatersberg Goldfield are also preferentially located in the Klapperkop Quartzite Member and overlying shales of the Timeball Hill Formation, Transvaal Supergroup. The rocks do not appear to form a particularly favourable protore but rather represent a favourable depositional site. The competency contrast of the shales, siltstones and sandstones in this stratigraphic interval is regarded as being important in facilitating vein formation, and the zone is also characterized by a high Fe2+/Fe3+ ratio and high C content, which may have reduced the mineralizing fluids and caused gold to precipitate. Fluid inclusion data show the quartz veins formed at 250–330 °C and pressures of 1.3–1.75 kb, from CaCl2-rich brines. Similar controls may also have favoured gold enrichment in the Cape Supergroup.
The Southern lower Karoo rocks have a potential for gold mineralization (higher degree of metamorphism, higher fluid temperatures and intense deformation during the Cape orogeny creating suitable trap sites). This conclusion is supported by historic workings in southern Karoo rocks, Cape Supergroup and basement rocks. In our opinion the gold mineralization has never been sufficiently explained and investigated.
The Western lower Karoo rock has a potential for base metals, specifically Pb and Zn as well as Vr, Cr and potentially Ni (as a result of source material and the composition of the volcanic component in the east).
Discussion.
Paramount to any discussion on the gold mineralization in the Western Cape Province is the question of why investigating the potential of Au in the province should be of importance. It is evident that the geopolitical scenario in the world is undergoing profound changes, the outcome of which is completely unknown. In addition, the effect of climate change on agricultural ventures and societies in general is equally unpredictable. As a consequence of these changes, the concept of “globalization” seems to be under pressure. In short, it is SearchMin’s opinion that to have a fundamental register of assets will become a critical bargaining chip in future. There are of course many negative issues related to mining in the Western Cape. Under current conditions the weight of the decision to mine any commodities in the province is, in our opinion, clearly to avoid mining, mainly due to environmental issues. This may however not be the case in the future. Thus, understanding deposits in the province is fundamental importance, provided:
The process is scientifically approached.
The work is independently conducted.
Planning and/or executing gold exploration in the Western Cape Province is not a simple matter from various perspectives:
The Province is host to a huge variety of ecosystems that are under extreme pressure as a result of urbanization and agricultural activities.
Many of these ecosystems are unique and highly sensitive.
South Africa is a developing country. This fact and a variety of complex political issues renders knowledge regarding existing mineral deposits and mineral deposit with future exploration potential essential for the country. Exploration should be done in a professional way with the utmost sensitivity to the various issues at hand.
As illustrated in many African countries, expectations around commodity potential in a specific area may lead to disastrous exploitation and consequent ruining of not only a valuable resource, but also the destruction of societies and the ecosystems in the vicinity of such uncontrolled mining. This needs to be avoided at all cost, especially in the Western Cape Province scenario. For this reason locations are not discussed in this document.
From a geological viewpoint the facts provided in this discussion illustrates the complexity of gold mineralization and accompanying that, the challenges in exploring for potential deposits.
Notwithstanding points 1 to 5, developments in exploration techniques over the last decades enable exploration to be conducted in a responsible and sustainable manner. Key to this is:
The involvement of professional independent personnel in the planning of each phase of any exploration program, commencing with non-invasive exploration.
A phase by phase approach where the results of each phase is thoroughly evaluated prior to the planning and execution of the following phase.
The legal backing to halt an exploration with immediate effect if:
the results are marginal and/or
the influence on all affected role players and ecosystems cannot be agreed upon or is in doubt.
the deposit proves to be of such a nature that mining can not be reconciled with the demands of the environment or the community in the vicinity.
A political scenario where decision making will be based on scientific facts and results and not ideology.
The involvement of investing companies with a proven track record and the financial capability of funding eco sensitive exploration, the life of mine sustainabilty as well as mine rehabilitation phases of the project prior to commencement of exploration.
As discussed above, gold enrichement is evident over a large time period and a spectrum of geological settings in the Western Cape Province. Sufficient evidence exists to suggest that finding a sizeable gold deposit is not unrealistic. In short the various possibilities are:
Group A
A1: Au in the “Swartland Group” predating granite intrusion and localised in quartz veins along faults and fractures and possibly other trap sites.
A2: Au within or in proximity to hydraulic breccias associated with Aa type CGS granites.
A3: Gold related to Sa2 type granites, either within the granite or in trap sites in the Malmesbury Group surrounding high level intrusive phases.
A4: Gold related to Ca- or Mg- skarns associated with Ia type Cape granites.
A5: Mesothermal gold related to mafic to intermediate CGS plutons.
Group B
B1: Gold on the contact zones of Sa1 (possibly Sa2) granites of the CGS and the Malmesbury Group.
B2: Gold in sheared Sa2 CGS granites, shearing possibly related to the Cape Fold belt event.
B3: Gold in close proximation to the uppermost sections of the Kaaimans Group/Malmesbury Group and the overlying Table Mountain Group.
B4: Gold related to quartz veins within the lower portions of the Table Mountain Group.
B5: Gold entrapped in quartz veins in the Bokkeveld Group or possibly trapped within fold hinges in the Bokkeveld Group.
B6: Gold weathered from top zones of hydrothermal breccia pipes and redistributed in sediments.
B7: Reworked gold in recent sediments, mainly reconcentrated from previously exposed Malmesbury Group/CGS contacts during drop in sea levels and/or recent weathering surfaces.
An important aspect pertinent to the economic potential of mineral showings in the Western Cape Province is to emphasize the effect of geological events post granite intrusion and deposition of the Cape Supergroup. It has been illustrated recently (31) that not only only NW-SE shearing and faulting should be considerd but the formation of horst and graben structures by NE-SW faulting during the late Cretaceous tectonic inversion tectonics.
The discovery of the W-Mo (REE) Riviera deposit near Piketberg illustrates the potential of base metal and gold mineralization associated with the Cape granite suite. Little doubt exist that metallization associated with “fertile” high level magmatism as well as volcanism does exist in other localities.
Any exploration program should be planned taking the environmental aspects into consideration as a first step, followed by delineating of potential areas based on favourable geological parameters.
Inquiries may be made in writing to:
R. Scheepers at the following E-mail address: admin@searchmin.com
References:
Please contact for references. admin@searchmin.com
