Vermiculite valley

Materials World magazine
,
3 Jan 2011
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Vic Fitzmaurice, CEO, Gulf Industrials, Sydney, Australia, discusses the properties of vermiculite and outlines his company’s mining activities in East Africa’s Rift Valley.  

Some naturally occurring minerals have direct application with the minimum of processing. This is because they either have a chemical reaction, such as potash as a fertiliser, or the mineral’s physical attributes convey a useful property in application. One such mineral is vermiculite, which results from the weathering or hydrothermal alteration of phlogopite and biotite mica.

Mica is an aluminium silicate that displays a distinctly platy nature due to its two tetrahedral for every octahedral sheet. When altered by either weathering or hydrothermal activity, the potassium ions between the molecular sheets are replaced by magnesium and iron ions. This gives vermiculite a unique property, for, when heated, (exfoliated) the mineral particle expands greatly as the mineralcontained water flashes into steam forming a wormlike structure.

The properties of vermiculite include ultralight weight for volume, the ability to absorb and retain water, the entrapment of large amounts of air when exfoliated and fire resistance. Consequently, vermiculite has a wide variety of uses (see below).

An added bonus is the grain shape of the exfoliated material that, ideally, should be cubic or some other equi-dimensional shape. For most applications, particle size is paramount, for it gives the maximum exfoliation and provides the best product.

Vermiculite mining is relatively simple, as it is a soft mineral and, therefore, usually only requires basic earth moving equipment. Processing includes milling to break-up the flakes, drying to a lower moisture content, removal of contaminants and foreign material, and screening to uniform flake sizes.

Some vermiculite deposits, according to geology, contain asbestos. For many years, one of the world’s largest deposits at Libby, Montana, USA, was used to make proprietary products. It was closed following a number of asbestosis cases that could be traced back to the Libby material. No vermiculite deposits containing asbestos can now be worked.

At the source

Genesis requires source rocks rich in mica, and fluids and gases that transform them to vermiculite. Such events occur in the emplacement of carbonatites – those rare carbonate-rich igneous rocks that are found mainly in rift environments. Early debate on their origin focused on re-melting of limestones in a silica-rich igneous event. More recent reviews indicate that the carbonate source was deep in the mantle, kimberlites, another deep-source rock, also contain these minerals.

Associated with carbonatites, often zoned around them, is massive peralkaline (aluminium poor, sodium and potassium rich) metasomatism (intense chemical alteration by gas and fluids) known as fenitisation. The area with the highest density of carbonatites is the Rift Valleys of East Africa.

Vic Fitzmaurice, CEO of Gulf Industrials, an Australian-listed company with a focus on industrial minerals in Africa, says, ‘We purchased the Namekara deposit from Rio Tinto in 2009. This deposit is part of the Ugandan Bukusu carbonatite located on a spur of the western Rift Valley. The complex ring type intrusion is marked by a ridge of high grade (22-41%) vermiculite of exceptional quality. It contains few impurities, large flakes and no asbestos.’

The deposit has a JORC compliant 54.9Mt resource statement, recently verified by SRK, Cardiff, UK. The consultancy’s report indicates 26.7% vermiculite in the +180μm fraction, and 18.8% vermiculite in the +425μm fraction range. This resource calculation is based on an outcrop of 1x1km (location of existing mine/pit) part of the 5x1km orebody identified by exploration. It is, the report adds, one of the largest high-grade (large crystal size) vermiculite resources in the world.

‘The deposit has a production history that had been allowed to lapse, notes Fitzmaurice. ‘By 2010, Gulf had refurbished the plant to a capacity of 10,000t/y, assisted by US$1m financial support from UK Dupré Minerals Ltd. This is on top of a 25-year exclusive sales agreement for all of the mine’s product.’

‘There is a great demand for the large Namekara flakes,’ says Fitzmaurice. ‘Although Africa accounts for 40% of world production from the South African Palabora mine, due to mine future depletion its product is now like those from the USA, China and Australia and confined mainly to fine grain sizes.

Optimistic forecast

Gulf Industrials began production in Mid-2010 with 1,000t sold in the quarter. ‘We were fortunate that many of the risks associated with beginning a new mining operation were ameliorated by the past work carried out by Rio Tinto,’ remarks Fitzmaurice. Rio Tinto’s exploration programme included drilling 64 holes for resource definition, pit optimisation and design, plant redesign, transport and infrastructure studies, and market research. The vermiculite deposit extends from near surface to a depth of between 45m and 55m and is excavated using standard excavators in a shallow open pit operation.

Anticipated production for the first year of steady state operations by Gulf Industrials will be 10,000t, building up to 16,000t per annum. Expansion plans underway will lift the output to 30,000tpa by mid 2011, claims the firm.

As with all industrial minerals, transport to market is a major component in the business plan. Namekara is located near the Kenyan border with a direct road link to the port of Mombassa. The closest rail spur is 12km from the mine, and the closest major station on the Mombasa railroad is at Tororo, 35km from the mine. An agreement has been reached with an East African freight and logistics company SDV Transami for the transport of all concentrate production from the mine.

‘We are negotiating for a complete service at a very competitive rate. Uganda is 2,500km nearer the European markets than the South African competition,’ declares Fitzmaurice. ‘Gulf Industrials has forward orders from Dupre for around 150,000t of high-grade material over the coming year. In addition that will take some time to fulfil, but we are intent on increasing capacity to 30,000t over the next two years. In addition, we plan to raise funding to build at least one modular 50kt/yr plant to increase the mine’s output to over 80kt/yr in the near future.’   

Vermiculite uses and markets

Uses – Loose-fill construction insulation, high-temperature insulation when moulded with sodium silicate, insulation of AGA cookers, cementitious spray fireproofing, fire-resistant wallboarding, the manufacture of light-weight concrete, and light weight packaging. It can also be used to absorb chemical spills and in explosives as a blast mitigant. In agriculture, it is used to retain water in the soil and improve its texture. The extreme use is in hydroponic cultivation. Other uses include brake linings and gaskets.

Market report – According to the United States Geological Survey, the world annual consumption of vermiculite is around 550,000t. Three countries account for 84% of this total – South Africa (40%), China (24%) and the USA (20%). Global consumption by sector is not known but, in the USA, 36% is used as lightweight aggregate, 30% in soil conditioning and as a carrier for slow release fertiliser, 26% in horticulture, and eight per cent in insulation. The current price of vermiculite is between about US$300/t and US$500/t delivered, with the higher price reflecting larger particle sizes.  

Further information

Vic Fitzmaurice, CEO, Gulf Industrials, Level 10 Gold Fields House, 1 Alfred Street, Sydney NSW 2000, Australia. Tel: +61 2 8247 5333. Fax: +61 2 9247 7722. Website: www.gulfindustrials.com.au