Applied Earth Science: Transactions of the Institutions of Mining and Metallurgy

As an external consultant advising industry (mainly the mining industry), two contrasting experiences are frequent. One is that the industry practitioners have strong domain knowledge that the consultant lacks. The other is that the industry practitioners often suffer from paradigm paralysis, using models of thinking that are either fundamentally inappropriate, or, perhaps more commonly, have become inappropriate through the passage of time and changes in technology and computing power. Although, and perhaps because, the data available have often grown considerably, paradigm paralysis can cause decision makers to fail to make full use of the available information, or worse, can lead to outcomes contrary to those intended. By coming in as an outsider, external consultants can provide benefit by introducing new paradigms or updating previous paradigms, subject to the important proviso that they become familiar with the domain knowledge and work closely with the industry practitioners. In this paper, the author discusses a number of projects, in which he has been involved, which illustrate the occurrence of paradigm paralysis.

The four metals of economic significance in the Central Africa or Great Lakes region, i.e. gold, tin, tantalum and tungsten, are part of one composite metallogenic system that operated about 980±20 Ma. The main driving agent was peraluminous ilmenite-series granite magmatism, synchronous with intracratonic compression and associated with the final amalgamation of the supercontinent Rodinia. The granitic melts were emplaced at intrusive levels of ≥2 kbar (≥8 km); the intrusions display a variable and often advanced degree of fractionation, including abundant Sn–Ta–Li–Be–Rb–Cs pegmatites, and are associated with hydrothermal systems enriched in tin, tungsten and/or gold. Based on cumulative past production and present metal prices, gold in hydrothermal quartz veins is the major commodity, followed by tin either in rare metal pegmatites or in sheeted, hydrothermal quartz veins. Many deposits in the province occur in siliciclastic metasedimentary, or metabasaltic roof rocks above parental granites; mainly in its western part, the zone of mineralisation retracts into the granite roof. Typically in the first case, antiformal sites acted as fluid escape zones, with carbonaceous or metabasaltic rocks as chemical traps for tungsten and gold. Examples of pegmatitic and magmatic–hydrothermal deposits are presented in some detail in order to illustrate characteristics and genetic controls, and to support the metallogenic hypothesis here advanced. Impeding strategic exploration, published elements of understanding the evolution and mineralisation of the Kibara belt are contradictory and essential links are missing, foremost an understanding of the 1 Ga flare up of fertile granites. Towards solving this conundrum we suggest that the key is delamination of the mantle lithosphere and dense mafic lower crust, residual after extraction of voluminous 1·38 Ga granitic melts. During pan-Rodinian orogenic events, the Tanganyika spur of the Tanzania craton acted as an indenter whose impact caused foundering of the early Kibaran lithosphere. Consequent influx of asthenospheric heat triggered large-scale crustal melting that resulted in the tin granites. The stress state was largely compressive but possibly punctuated by short or local extensional events. The correlation of geological evolution and mineralisation substantiates the formal recognition of a Kibara Metallogenic Domain, which is composed of two units: The Mesoproterozoic (1·4 Ga) Kabanga-Musongati nickel (±copper, cobalt, platinum) province; and the early Neoproterozoic (1 Ga) Kibara rare metal and gold province that is the main subject of this paper. The present understanding of the operating metallogenic systems remains limited. Regarding the application of modern concepts and technologies, this province is drastically underexplored.

Rare earth elements (REEs) have a crucial role in modern environmental and medical technologies, leading to a continuously growing demand for these elements. The relatively modest scale of the global REE mining sector means that the REE mineral deposit type knowledge base is small compared to more well-known styles of mineralisation. In this paper, we present a new classification scheme for differing REE mineral deposit types, outline the geological processes that cause REE enrichments, define characteristic grades and tonnages, and provide information on the environmental impact associated with REE mining, extraction and processing. Although current global REE supply is dominated by production from carbonatites, REEs are in fact found in a wide variety of deposits, including magmatic alkaline complex- and rhyolite-hosted REE mineralisation, REE-enriched iron oxide-copper–gold deposits, and REEs within heavy mineral sands, amongst others. Critically, REE mineralogy is linked to environmental risks during mining and refining, especially aspects such as radioactive U–Th, the use of harmful chemicals during processing and greenhouse gas emissions; future REE supply therefore needs to consider and address these environmental risks.

The metalliferous intrusive complexes in the Khentii Uplift evolved post-collisionally in an intracontinental environment. Their felsic magmatic rocks are surrounded by a small marginal facies of more granodioritic to monzonitic composition and were attributed to the A2 type granites, based on discrimination diagrams using K, Na, Si, Nb, Y and Rb. These rare metal granites have elevated contents of fluorite, topaz and tourmaline and are characterised by the light rare earth element enriched minerals allanite-(Ce) and monazite (Ce) prevailing over the xenotime, which is the only host with heavy rare earth element enrichment in these Mongolian granites. Together with zircon, these heavy minerals also show up in the clastic apron around these granites under study, providing a clue to the temperature of formation when the intrusive bodies were emplaced, and moreover provide a tool for exploration in pegmatitic and granitic terrains. Albite alteration is associated with a moderate U–Th–Ti mineralisation and greisen bodies were enriched in Sn and W of subeconomic grade. Only cassiterite re-appears as a heavy mineral in alluvial–fluvial placer-type deposits around the granite stocks, whereas only W occurs in a wide range of limonite and leucoxene like minerals. Sn-, W-, Fe, Mn- and Ti-bearing chemical residues can be used as a short-range marker to pinpoint the loci of enrichment of Sn and W, whereas the aforementioned heavy minerals are applicable as long-range tracers for metalliferous A-type granites. The Pb–Cu–Zn mineralisation is rather homogeneous and of little value as an exploration tool. Three different stages characterised by REE-carbonates and kaolinite, metalliferous duricrust abundant in Sn, W and Ti and aluminium–phosphate–sulphate minerals developed under oxidising conditions. The way how fluids moved though the granitic rocks, either as per descensum or per ascensum fluids, cannot be determined precisely. Therefore epithermal processes cannot be ruled out and have been held responsible for this near-surface alteration zone superimposed on a high-temperature Sn–W mineralisation in the Late Triassic to Early Jurassic A-type granites. These intrusive rocks are related to an extensional regime of the Triassic Indosinian orogeny in southern China.

In response to the implementation of a new schedule for iron ore fines in the International Maritime Organization's International Maritime Solid Bulk Cargoes Code, improved measures for the management of moisture have been developed. In particular, prediction of cargo moisture allows management of iron ore fines within the supply chain to facilitate the safe shipping of iron ore fines. An Autoregressive Integrated Moving Average model, augmented to allow for shipment tonnage, has been developed to predict the moisture level from previous shipments of the same product. The model explains about 60% of the moisture variance. It was found that inclusion of other available information, such as ore composition, train/rake assays and recent rainfall at port and mine did not add to the predictive power of the model.

Descriptions of the Witwatersrand goldfields have invoked superlatives around themes including great wealth, huge depths, giant mines and innovative engineering. After its discovery in 1886 and further discoveries in the 1930s and 1940s, the Witwatersrand dominated world gold peaking at 1000 t Au production in 1970. There has been a steady production decline since 1970, and, although the trend is clear in hindsight, few people predicted the seriousness of the fall in production or the grave situation of the industry today. The annual decline of Witwatersrand production has averaged 20 t of gold per year since 1994; at this rate, Witwatersrand gold mining will end in mid-2022. The forty-year production decline is attributed here to exploration failure as there has been no new goldfield discovered since Evander in 1951. A lesson from many of the world's great goldfields is that, where much gold has been discovered, there remains opportunity for repeats and additions by using new ideas and technologies. Future Witwatersrand exploration could adopt multiple working hypotheses rather than a single exploration model, introduce high-level geoscience training that is appropriate for a range of potential exploration models and strategies, and encourage a mindset in which discovery becomes both imperative for the whole community and an all-guiding passion. New exploration models open new opportunities not considered and tested over the last 60 years.