Geology of the Steenkampskraal Monazite Deposit (SMD)
The monazite deposit occurs within the Bushmanland Terrane of the Namaqua-Natal Metamorphic Province of Southern Africa and forms part of an intrusive suite emplaced during the 1,100Ma aged Namaqua orogeny and associated regional metamorphic event. The emplacement of the narrow (0.02m to >10m thick) monazite vein is structurally controlled and occurs along a strike length of 1,200m to a known depth below surface of 160m. The intrusion is considered to have formed through the development of an REE-enriched immiscible liquid through fractional crystallisation of a granitic magma or partial melting of a thorium-enriched granitic progenitor.
The target mineralised monazite vein strikes east-west across the Steenkampskraal Mining Right area and morphologically is a thin lenticular body, which in three dimensions, appears as a step-like intrusion with dips varying from almost horizontal to 70° as the horizon “steps downwards” in a southerly direction. The vein undulates and boudinages resulting in variable true thicknesses and is both laterally and vertically continuous. The mineralisation is constrained by known east and west bounding faults but the structural and geological framework is such that potential mineralisation, displaced by tectonic events, could exist beyond the bounding faults.
The TREO+Y2O3 grades (14% TREO+Y2O3 in situ) of the monazite deposit are high for typical REE deposits and vary from 0.40% to 46% and are typically dependant on the quantity of diluting minerals within the mineralised monazite vein. The grade distribution has historically been considered relatively consistent throughout the deposit. A geochemical 3D modelling exercise has recently shown that Th-REE enriched pockets exist that can be specifically targeted early during mining.
A total of 28,110 meters of exploration drilling has been done from 232 HQ and NQ core holes at a nominal drillhole spacing of approximately 25m. In addition, 1,700 assay and geochem samples from drilling, excavation (surface tailings and rock dump), and underground channel samples were collected since the start of resource evaluation activities.
A high-resolution airborne Magnetic and Radiometric Survey has been completed over the naturally-occurring radioactive material (NORM). Ground geophysical surveys for detailed hydrogeological and structural investigations (structural model) were also completed. The deposit has a known strike-length of 1,200m and down-dip extension of up to 160m locally. To date, mineralisation is only locally open down-dip and potentially open along strike to the northeast and west.
Mineralisation of the Steenkampskraal Monazite Deposit (SMD)
Mineralisation is dominated by monazite, varying mostly due to syn-emplacement dilution by host rock and post-emplacement contamination by sulphides, magnetite and silica. The TREO grades are typically dependent on the quantity of diluting minerals. The mineralized monazite vein and mineral monazite is, to varying degrees, associated with:
- REE-barren intermixed apatite.
- Lesser amounts of thorite, REE-bearing allanite and xenotime.
- Internal dilution including granitic xenoliths, quartz, magnetite, sulphides, galena and alteration minerals including chlorite and ilmenite.
Significantly Improved Resource Allocation at SMD over recent years
- 93% of the total resource tonnage reported to Measured and Indicated resource categories.
- An almost threefold (271%) increase of contained TREO + Y to 86,900t from the 2012 resource estimate.
- Improved Geological Model with detailed structure (12 individual fault 3D wireframes) was utilised to greatly enhance the domaining of the deposit for more accurate mine planning and grade estimation purposes.
- The more detailed domaining and higher sample density also gave greater levels of confidence in the allocation of resource tonnages to the Measured and Indicated categories, (inferred to measured or indicated, indicated to measured).
Hydrogeology Drilling and Pump Testing Programme on the SMD Mining Right
- Data and facilitation support for all onsite hydrogeological activities have been completed, confirming sufficient water supply for the mine and plant.
- Conceptual Hydrogeological Model, Ground Water Flow and Mass Transport Model (Numerical Flow Model), Source Term Characterisation (geochemical study) and Design Assessment have been completed.
- Borehole water and mine dewatering can supply the water requirement of 1000 m3/d for more than 30 years, which is the present estimated life of the mine.
Geotechnical Investigations Completed on the SMD Mining Right
These investigations study the physical characteristics of the rock (such as rock strength and failure potential). These studies determine the underground support and influence the design of the plant foundations.
Prospecting Right Activities
- A Gridded Radiometric Scintillometer Survey has been completed to delineate possible shallow subsurface monazite extensions at Uilklip and Roode Wal.
- 11 surface channels were cut on previously disturbed ground that provided 126 samples for assay (incl. 2.65 m @ 37.32% TREO + Y2O3).
- The Airborne Radiometric and Magnetic Surveys greatly contributed to the selection of monazite targets over the Prospecting Right area. The Magnetic Survey further assisted in the understanding of the structural characteristics of the Steenkampskraal orebody and the underground water potential.
Possible Future Work on the Steenkampskraal Mining and Prospecting Right Areas
- Drilling – Down-dip extension on the Mining Right.
- A soil-orientation study for possible soil geochemical sampling. This is a study done to test various methods and depths where geochemical sampling of the regolith can indicate subsurface mineralisation. It is a relatively inexpensive method used in areas of thick soil cover as in valleys where radiometrics are unable to detect mineralisation below a depth of ~20cm.
- The gravity geophysical method can also be used to identify extensions to the current orebody on the Mining Right and to explore anomalous areas on the Prospecting Right. This method has been used with considerable success in similar emplacement settings.
- Soil sampling/drilling – north-eastern extension due to N-S trending normal faulting.
- Drilling north of the Steenkampskraal outcrop to explore for the northern limb of the steep structure. In the structural paper it is hypothesized that the monazite vein sits within a “fold structure” (steep structure) with two limbs pointing downwards to the south and to the north (our known mineralisation sits in the southern limb). There is therefore the possibility of mineralisation in a limb that is north of the outcrop on top of the koppie.
- Drilling – Uilklip/Roodewal.
- Soil sampling of the airborne anomalous areas.
- Drilling anomalies 2 and 42 on the farms Rietkloof and Tafelberg respectively.
- Possible regional soil sampling.