Borehole radar is a short-range, high-resolution geophysical technique that can be used to delineate the position of the Merensky platinum reef in underground mines situated in the Western Bushveld Complex. In this study, borehole radar is used in reflection mode from four boreholes drilled sub-parallel to the expected position of the Merensky Reef within an underground mining block bounded by two cross-cuts and a haulage. This study relates the stratigraphic column at Amandelbult Section to borehole radar reflectivity. The radar illumination line coordinates produced along the Merensky Reef surface are used to construct a three-dimensional surface of the reef within the defined mining block. The geophysical interpretation presented here shows how a slump in the Merensky Reef, called a pothole, is imaged using borehole radar. This study analyses the increase in geological confidence related to the improved delineation of the elevation of the Merensky Reef. The financial impact of using borehole radar to delineate this pothole is analysed at the various mining steps, namely: orebody definition, mine planning, mine development, ore extraction and ore processing. The information gained by conducting borehole radar is compared with the information acquired using only standard geological drilling. This study concludes that the application of borehole radar significantly increases the confidence in the geological model prior to mining. Conducting borehole radar prior to mining improves mine planning and development, ensures that less waste is mined, facilitates the effective deployment of labour crews, prevents waste being sent to the processing plant and avoids deferring income until a later date. Recommendations are made on how to plan for and include borehole radar in the mining process. / Dissertation (MSc)--University of Pretoria, 2009. / Geology / unrestricted

PhD, Faculty of Engineering and the Built Environment, University of the Witwatersrand, 2010 / The aim of this investigation was to provide a proper design procedure for Merensky crush pillars, based primarily on underground measurements. Three sites with a variety of geotechnical conditions were selected. An interaction between the pillars and the rock mass around the stopes was shown by the literature, relevant laboratory tests and numerical modelling. During the investigations, nonlinear rock behaviour was observed at one of the sites. Further studies revealed that nonlinear behaviour also occurred in samples extracted from high stress conditions at the other sites, but the rock mass was not nonlinear at these sites. A methodology for determining stress from strain measured in nonlinear rock was established. The research also established that there is an approximately linear relationship between peak pillar strength and w/h ratio at ratios between about 1.2 and 8. The so called ‘squat’ effect is not observed because pillar failure is not contained within the pillar but extends into the foundations. A linear peak pillar strength formula was established from back analyses of underground pillar failures and was confirmed by numerical modelling. Pillar behaviour was established from underground measurements on one stability pillar and six crush pillars, which included peak and residual strengths. Also, stable and unstable loading conditions were established from an analysis of pillar bursts and the minimum strata stiffness for stable pillar failure was determined. This stiffness is only achieved near the advancing face and pillars that fail in the back areas are likely to burst. For this reason, pillar design needs to include the peak strength as large pillars may be too strong and fail in the back area. The residual strength also needs to be considered as the load-bearing capacity of these pillars needs to satisfy the criterion of 1 MPa across the stope to prevent back-breaks. This translates into a pillar stress of between 8 MPa and 13 MPa if the pillar lines are spaced 30 m apart. The peak and residual requirements have been included in a design chart, and the relationship between w/h ratio and residual strength is provided in a graph for easy design.

M.Sc. / This study focuses on the Merensky Reef (MR) occurring within the Two Rivers Platinum mine property in the farm Dwarsriver 372 KT, on the Southern sector of the Eastern Limb of the Bushveld Complex. Five MR exploratory drill core intersections were obtained. Petrographic and mineral chemical characteristics of these drill core samples focused on the characterization of minerals like clinopyroxene, orthopyroxene, plagioclase, chromite and olivine. Data of the cryptic variation of orthopyroxene, plagioclase and chromite, from a 10 m interval (approximate thickness of the section studied); from footwall through the MR to the hangingwall lithologies at Dwarsriver are described in this study. Locally the vertical cryptic variation of these minerals is broadly consistent with regional trends of the RLS. The lateral variation (i.e. along strike) is less pronounced; however, locally these minerals appear to be chemically evolving moving to the south of the property. Footwall orthopyroxene compositions vary from a minimum of En66 and reach a maximum of En84. Those of the MR range from En71 to En85. Hangingwall orthopyroxene compositions range from En60 and reach a maximum of En80. Plagioclase compositions in the footwall units range from a minimum of An69 and reach a maximum of An85. Those of the MR range from a minimum of An35 to a maximum of An84. This wide range in plagioclase compositions is believed to be as a result of the increased presence of fluids within the MR interval. The hangingwall plagioclase compositions range from An64 to An84. By analogy of the Western Limb, where the lithologies of the Northwestern sector are believed to be proximal to the feeder of this limb; the local lateral variation in the present study suggests that the lithologies of either the Central or Western sectors are most probably proximal to the feeder for the Eastern Limb. PGM assemblages associated with and adjacent to the MR chromitite stringers were evaluated using an MLA. Data obtained from this technique is in broad agreement with regional studies of the MR. With the aid of wholerock PGE assays the MLA technique has proven to be a powerful tool in evaluating PGM assemblages relatively quickly, from a few carefully selected samples. The mineralogical associations of the PGM with the gangue and host minerals have shown three main associations. These are the associations of chromite, BMS and silicates with the PGM, of which the base metal sulfide (BMS) association is remarkable given that these have a relatively low modal abundance. The relatively high mineralogical association of the BMS with PGM has been explained by a model involving a base metal sulfide liquid which possibly scavenged chalcophile and siderophile elements. Chromite chemistry and modal analyses of MR secondary silicate phases, which peak adjacent to the chromitite stringers, suggests elevated fluid overprinting within and adjacent to the chromitite stringers. The upper chromitite stringers, however, have higher abundances of PGM phases that are believed to be secondary in origin relative to the basal chromitite stringers. Generally the PGM associated with the upper chromitite stringers are also bigger in size averaging 70 μm as opposed to 27 μm for those associated with the basal chromitite stringers. The increase in grain size of the PGM along with the higher modal abundance of secondary PGM phases associated with the upper stringers is believed to be as a result of fluids. These fluids although affecting both the upper and basal chromitite stringers, appear to have had a relatively higher influence on the upper chromitite stringers. The most common PGMs encountered in this study are isoferroplatinum, sperrylite, michenerite, maslovite, cooperite, laurite and braggite.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: It is widely accepted that sulphide is the carrier and concentrator of PGEs during magmatic mineralization episodes in the Merensky Reef (MR). PGE concentration peaks and sulphide volume percent peaks are very closely correlated. Koegelenberg, (2011), showed in an experimental investigation that sulphide movement through a cumulate silicate and cumulate oxide pile behave in such a way that sulphide melt gets trapped in chromitite layers. When looking at the compositional distribution of sulphide within the MR it is noted that not only does the sulphide volume percent varies with MR stratigraphy but also the sulphide composition. Sulphide composition is more Cu-rich in the chromitite layers and more Fe and Ni dominated in the hanging wall to the chromitite layers. Until now the more Cu-rich assemblage of the chromitite layers are accepted to be of a sulphide melt composition compared to the Fe and Ni dominated Monosulphide Solid Solution or MSS composition in the hanging wall. In this study we used an experimental approach with a sulphide starting composition thought to exist as the parental sulphide composition of the MR to investigate the phase relations with changing temperature. It is found that the sulphide composition in the chromitite layers represent a sulphide melt composition at 1000 ± 50ºC. At 1000ºC, 50% of the sulphide system would exist as a melt. This Cu-rich melt would have segregated from the MSS and be trapped in the chromitite layer. Also at 1000ºC the partitioning of the Pt would have induced a secondary enrichment step of the Pt concentration in melt through the partitioning of Pt between a sulphide melt and a sulphide solid phase. The experimental evidence in this study points towards a possible source for the parental sulphide magma to the MR, which could have been a slightly Cu enriched mantle sulphide composition. Also, the secondary enrichment of Pt through sulphide melt fractionation at 1000ºC plays an important role in the shaping of the ore body. / AFRIKAANSE OPSOMMING: Dit word wydliks aanvaar dat die sulfied fraksie van die Merensky Rif (MR) die draer en die konsentrasie agent is vir Platinum Groep Elemente (PGE`s) gedurende mineralisasie episodes. PGE konsentrasie en sulfied volume persentasie is op `n hoogtepunt by gelyke stratigrafiese posisies in the MR. Koegelenberg, (2011), het deur middel van eksperimente bewys dat `n sulfied smelt deur `n voorafbestaande kumulaat laag kan beweeg en dat veranderende fisiese eienskappe tussen sulfied smelt en silikaat kristal en sulfied smelt en chromiet kristal, die sulfied smelt sal opsuig en verhoud om verder deur te suipel. Dit is egter oplettend dat nie net die sulfied volume persentasie varieer as `n funksie van die MR stratigrafie nie, maar ook die sulfied samestelling. Die meer Cu-ryke sulfied samestelling in die chromiet lae word aanvaar as `n sulfied smelt fraksie en die meer Fe en Ni dominerende sulfied samestelling in die oorhangende wandgesteentes verteenwoordig die Monosulfied Vaste Oplossing (MVO) soliede fase. In hierdie studie maak ons gebruik van eksperimentele petrologie tesame met `n begin samestelling verteenwoordigend van die oorsprong sulfied samestelling van die MR, om die fase verwantskappe van hierdie spesifieke samestelling te ondersoek. Dit word gevind dat die fraksionering tydens die vorming van die MR plaasgevind het by ongeveer 1000 ±50 C. By hierdie temperatuur is 50% van die sisteem teenwoordig as `n smelt fase. Hierdie Cu-verykte smelt was daartoe instaat om deur die silikaat laag te suipel, geskei te raak van die Fe en Ni dominerende MVO en vasgevang te word in die chromiet lae. Hierdie fraksionering van die sulfied smelt het ook `n sekondêre effek gehad op die verspreiding van Pt tussen sulfied smelt en sulfied soliede fases. Hierdie eksperimentele bewyse dui eerstens op die moontlikheid van `n sulfied smelt in die MR wat sy oorsprong vanuit `n effense Cu-verykte mantel bron kan hê, en tweedens op die belangrikheid van `n sekondêre proses vir Pt re-distribusie tydens die vorming van die MR.

Student Number : 0201438A - PhD thesis - School of Geosciences - Faculty of Science / This project focuses on the Upper Critical and Lower Main Zones in the eastern Bushveld Complex, South Africa. Lithological and stratigraphic information show that there are distinct differences at this level between the eastern and western limbs of the complex. Geochemical studies are centred on the Merensky and Bastard Cyclic Units in which the platiniferous Merensky Reef occurs. A major geochemical hiatus occurs in the Bushveld Complex at the level of the platiniferous Merensky Reef, close to the Critical/Main Zone boundary. The origin of this hiatus and its relation to mineralisation has not been fully resolved. Geochemical parameters are investigated that allow minerals in the Merensky and Bastard Cyclic Units to be classified as originating from either Critical or Main Zone magmas. Modelling of element ratios (Ni/Y, Cr/Ni, Cr/Co, Y/Co, Cr/V, Co/V and Cr/MgO) demonstrates the varying reliability of using ratios as geochemcial tools to constrain magma influxes within a chamber. However, it is shown that the Cr/MgO ratio is effective in determining real differences across the Critical/Main Zone boundary that are independent of lithology. In addition, initial Sr isotope ratios for plagioclase are significantly different in Critical and Main Zone rocks. Geochemical data through the Merensky and Bastard Cyclic Units indicate that orthopyroxene that originated from magma with composition like that of the Critical Zone magma sometimes occurs together with plagioclase that originated from Main Zone magma. In detail, in the pyroxenite at the base of the Merensky Unit, both plagioclase and orthopyroxene display Critical Zone signatures, but in the overlying part of the Merensky Cyclic Unit, plagioclase increasingly shows a Main Zone signature, whereas orthopyroxene continues to display a Critical Zone signature. Similarly, in the Bastard pyroxenite, Sr isotopes and absolute Sr in plagioclase display a range of values from Main Zone to Critical Zone, but orthopyroxene consistently displays Critical Zone affinity. These observations of mineral disequilibrium clearly show that the two major minerals in the Merensky and Bastard Cyclic Units were formed from two different, but coexisting, magmas. A model that accounts for this disequilibrium is proposed here. It invokes the influx of Main Zone magma at the level of the base of the Merensky unit that dispalced the Critical Zone magma upward, but the two magmas did not mix. The latter continued to crystallise orthopyroxene which sank through the Main Zone influx, due to its density contrast. These crystals collected on the crystal pile to form the Merensky pyroxenite. The Main Zone magma, into which the cumulus Critical Zone orthopyroxene accumulated, crystallised interstitial plagioclase that had a Main Zone Sr isotopic ratio. Whole-rock, major element geochemical data show that a variable proportion of the plagioclase in both the Merensky and Bastard pyroxenites is cumulus. It is inferred to have accumulated with orthopyroxene and has a Critical Zone initial Sr isotope ratio. Thus the two pyroxenites now yield a mixed Sr isotopic signature of Critical Zone cumulus and Main Zone intercumulus and possibly cumulus plagioclase that varies along strike. Above the two pyroxenites, the Sr signature of the norites and anorthosites of both cyclic units is dominated by cumulus plagioclase from the Main Zone magma. It is concluded that the variations in initial Sr isotope ratios do not result from mixing of magmas, but result from accumulation of orthopyroxene and plagioclase from a higher, isotopically distinct layer of magma into an underlying layer. The Merensky and Bastard Cyclic Units therefore display features of Critical or Main Zone magma characteristics depending upon which chemical parameter is considered. These cycles are therefore classified as a Transitional Unit.

Ph.D. (Geology) / Please refer to full text to view abstract

Thesis (M.Sc. (Geology)) -- University of Limpopo, 2022 / The Two Rivers Platinum Mine (TRP) located in the Eastern Bushveld Igneous Complex is currently exploiting platinum-group elements (PGE) in the Upper Group 2 chromitite (UG2) Reef at the Dwarsrivier Farm. TRP has acquired a new prospect (at the Buffelshoek Farm) and is currently planning to mine the UG2 Reef and potentially also the Merensky Reef (MR). Three drill-cores which intersected the UG2 Reef and MR at the Buffelshoek Farm made available by TRP were sampled for mineralogical studies using complementary techniques including reflected light microscopy, mineral liberation analyser and electron microprobe. The platinum group minerals (PGM) which host the PGE exhibit variability in their flotation rates and consequently variable PGE recoveries that is mostly attributed to the not so well understood PGM distributions and characteristics. The purpose of the study was to investigate the PGE process mineralogical characteristics such as the PGM phases, their modal abundances and mineral associations, as well as the grain size distributions within the UG2 Reef and MR at the Buffelshoek Farm. The observed PGM phases are broadly grouped into PGE sulphides, PGE arsenides, PGE bismuth-tellurides, PGE antimonides and PGE alloys. The PGM phases are largely dominated by PGE-sulphides (average of 80%) in the UG2 Reef and PGE-arsenides (average of 39%) in the MR. Although the UG2 Reef and MR are mineralogically different, the PGM observed are similar in composition, but vary in their proportions. The PGM are mostly associated with base metal sulphides typically, pentlandite in the UG2 Reef and silicates, which are dominated by amphiboles in the MR. The PGM grain sizes generally range between 2 and 22 microns in the UG2 Reef and range between 2 and 32 microns in the MR. The concentrations of platinum are the highest in both the UG2 Reef and MR, and with the platinum largely deported in PGE-sulphides (about 69 - 84.9%) in the UG2 Reef and PGE-arsenides in the MR. Palladium is mostly deported in the PGE sulphides (about 52.3 - 69.2%) in the UG2 Reef and mostly deported in PGE antimonides (about 43%) and PGE bismuth-tellurides (about 37%) in the MR. Rhodium (Rh) is entirely deported in the PGE sulphides in the UG2 Reef and deported in PGE sulphides (about 86.5%) and PGE bismuth-tellurides (about 13.5%) in the MR. Expected recoveries of PGM ranges from 76 to 89% for PGE sulphides and arsenides in the UG2 Reef and 61.3% in the MR, which is considered good. PGE bismuth-tellurides, PGE antimonides and PGE alloys are expected to be variably to poorly recovered, requiring suitable reagents to be well recovered both in the UG2 Reef and MR. / Faculty of Science and Agriculture Research Division Geological Society of South Africa North West University's School of Geo- and Spatial Science