The deposit has low thorium oxide levels for a rare earths resource and samples averaged 11 ppm thorium oxide per percentage of REO content. (Lynas Corporation Ltd, http://www.lynascorp.com).
Occurrences of thorium, yttrium and rare earth elements in Namibia are known to be associated with carbonatites and granites and pegmatites of Namibian and Mesozoic age. Placer deposits of these minerals have formed mainly in Tertiary to Recent times in the marine environment.
Thorium, yttrium and rare earth element mineralization associated with carbonatites
The Lofdal-Bergville carbonatite dykes and plugs.
The Lofdal-Bergville carbonatites are located 30 km west of Khorixas in Damaraland on the farms Lofdal 491 and Bergville 490, where syenite, porphyry, tinguaite, lamprophyre, fenite and carbonatite dykes and plugs have intruded Huab Complex gneiss.
The carbonatites are highly radiogenic and contain xenotime, bastnaesite and thorite. Other alkaline intrusives occur south of Lofdal 491 on the farm Oas 486. The Oas syenite intruded rocks of the Nosib Group.
atites on Lofdal-Bergville were investigated in 1982, and thorium and yttrium values from 0.17% to 14.4% ThO2 and 0.05% to 0.63% yttrium were obtained. In addition to the radiogenic minerals and calcite, the carbonatites contain limonite, hematite, magnetite, zircon, fluorite and apatite.
A sample of a carbonatite dyke assayed as follows: lanthanum 1.5%, cerium 0.87% and neodymium 0.74%.
Namibia Rare Earths files maiden Lofdal resource, confirms HREE
By: Henry Lazenby
Published: 26th September 2012
TORONTO (miningweekly.com) –
Namibia Rare Earths(NRE) had filed a maiden resource for its Lofdal rare earths elements project, confirming the presence of high levels of heavy rare-earth enrichment (HREE) in certain areas of the project.
The National Instrument 43-101-compliant resource estimate, covering Area 4 of the project located in the north-west of Namibia, pointed to “exceptional”
levels of HREE of between 75% and 93% HREE, depending on the cut-off grade, with corresponding total rare earth oxide grades (TREO) ranging from
0.27% to 1.26%.
What distinguishes the project from many other juniors that have entered the market in response to China’s reduction of exports over the past four years
– the country produces over 95% of the world’s rareearth’s supply – is its concentration of what are called heavy rare earths. “Given current rare-earth prices, over 90% of the value in this deposit lies in the four critical heavy rare
earths – europium, terbium, dysprosium and yttrium – with less than 2% of the value relating to lanthanum and cerium, the most common light rare earths,” NRE president Don Burton said in a prepared
statement.
Mining consultancy The MSA Group of South Africa prepared the estimate had identified the presence of an indicated resource, at a 0.3% TREO cut-off, of 900 000 t at 0.62% TREO, with 86% HREE, and an inferred resource of 750 000 t grading 0.56% TREO, with 85% HREE. The resource was drilled to a depth of 150 m and remained open at depth and along strike. At a low-grade cut-off of 0.1% TREO, the resource estimate provided for 2.88-million tons grading 0.32% TREO, with 76% HREE in the indicated category, and 3.28-million tons grading 0.27% TREO, with 75% HREE in the inferred category.
The company said it was still studying the most appropriate cut-off grade. NRE said a metallurgical study programme was also currently underway with Commodas Ultrasort, in Germany, and South African metallurgical specialist Mintek, to demonstrate the viability of extracting the rare earths from Area 4.
Burton also noted that subject to favourable outcomes on the metallurgy studies, the entire mineral resource at Area 4 could be upgraded from indicated and inferred to measured and indicated categories without any further drilling. However, there still remained substantial upside potential to increase the resource through further exploration of the 200 km2 Lofdal carbonatite complex.
The Halifax, Nova Scotia-based company debuted on the TSX in April, after it raised C$25-million in an initial public offering, in preparation for undertaking the resource estimate.
The Eureka carbonatite dykes
Monazite-bearing carbonatite dykes on the farm Eureka 99, located approximately 38 km west of Usakos, and about 2 km north of the Usakos-Swakopmund road, contain rare earth mineralization.
With the exception of a single occurrence of a sovite dyke, all the carbonatite dykes at Eureka are beforsitic in composition, but have varying concentrations of monazite.
The monazite-rich beforsites are characterised by rare earth oxide concentrations that range between 33% and 40%.
Drilling established proven reserves of 30 000 t of ore to a depth of 20 m, containing 1 900 t of rare earth elements.
The Kalkfeld Alkaline Complex
Thorium, yttrium and rare earth element mineralization is known to be associated with four carbonatite complexes in the Otjiwarongo and Grootfontein Districts. These complexes belong to a northeast-trending line of over 20 intra-plate-type, subvolcanic, ring complexes of the Damaraland Alkaline Province.
Within these complexes, thorium, yttrium and rare earth element mineralization is associated with late-stage plugs and dykes of mainly beforsitic composition, or with iron-rich, late-stage metasomatites. Three of the carbonatite complexes also carry disseminated pyrochlore.
The Kalkfeld complex is situated on the farm Eisenberg 78, about 11 km northwest of Kalkfeld, and measures about 5 km in diameter. The complex consists of confocal rings of granite, syenite, foyaite and carbonatite.
A plug of massive iron ore occupies the central area of the complex. The carbonatites and the iron ore show an enrichment in lanthanum (500 to 5 000 g/t), cerium (2 000 to 8 000 g/t) and neodymium (1 000 to 2 500 g/t).
The Ondumakorume Complex
The Ondumakorume Complex forms a prominent hill on the farm Etaneno 44, about 10 km northeast of Kalkfeld. In addition to syenite, nepheline syenite, volcanic breccia and iron ore, micaceous sovite, grey sovite and beforsite are the main types of carbonatite. Rare earth minerals such as monazite, ancylite, cerianite and carbocerianite occur within beforsite with whole rock concentrations of up to 9 000 g/t cerium.
The Osongombe Complex
Osongombe is the smallest of the Damaraland carbonatite complexes and is situated about 12 km southwest of Kalkfeld on the farms Osongombe 80, Sud Osongombe 83 and Okarume 82.
The diatreme consists mainly of volcanic breccia and beforsite together with iron ore. The beforsite occupies the central area of the complex and is composed of manganiferous ankerite, apatite-rich aggregates magnetite-siderite, quartz and accessory, finely disseminated, yellowish octahedra of pyrochlore.
The Okorusu Alkaline Complex
The Okorusu Alkaline Complex is situated 45 km north-northeast of Otjiwarongo. The complex is composed of a series of alkaline rocks including hortonolite monzonite, various syenites, foyaite, urtite, tinguaite, nephelinite and carbonatite.
The southern portion of the complex is characterised by the presence of various metasomatites including aegirine fenite, limonitic iron ore and numerous ore bodies of fluorite that were formed by replacement of dolomitic marbles.
The carbonatites at Okorusu occur as pluglike bodies and dykes that have variously intruded aegirine fenite, rocks of the metasomatic aureole and the central area of the complex.
On the farm Brandenberg 87 a number of beforsitic carbonatite dykes and carbonate fluorite- bearing metasomatites carry appreciable amounts of rare earth element mineralization of mainly pale yellowish-brown synchisite, green monazite and yttrio-fluorite. Some of the dykes are up to 20 m wide and can be followed for up to 300 m along strike.
Synchisite occurs as fibrous needle-shaped or as plate-like crystals and is mainly associated with carbonate-quartz-fluorite-barite-thorite-monazite and xenotime-bearing assemblages.
The total rare earth oxide content in the siliceous rocks varies from 1.5% to 7%. The thorium and yttrium values of these rocks range from 0.4% to 3.5% thorium and from 0.2% to 1.01% yttrium.
The Agate Mountain Carbonatite Complex
About 8 km northeast of False Cape Fria, on the north-western coast of Namibia, a carbonatite complex has intruded Karoo Sequence volcanics. Bastnaesite is associated with late-stage beforsitic (Mg-rich) carbonatite and occurs in irregularly distributed patches.
Thorium, yttrium and rare earth element occurrences associated with granites and pegmatites
Some of the post-tectonic biotite granites of late Pan African age and, in particular, Pan African pegmatites, are known to contain accessory monazite, gadolinite, allanite, thorianite and yttrio-fluorite.
Wlotzkasbaken allanite occurrence
Phenocrysts of allanite, up to 60 mm in length, occur in a coarse-grained Pan African granite northeast of Wlotzkasbaken, 30 km north of Swakopmund. The allanite crystals are extremely well disseminated and the granite has not been investigated for other rare eartk minerals or sampled for total rare earth content.
The Brandberg Alkaline Complex
Zoned allanite occurs in potassium metasomatised biotite granite of the Brandberg Alkaline Complex, whereas chevkinite, monazite and fluorite are commonly associated with potash-altered, biotite granite.
Peralkaline granites and sodium-rich fenites that are associated with the Amis complex, located on the southwestern periphery of the Brandberg complex, contain anomalous whole rock yttrium (up to 2 000 g/t) and thorium concentrations (up to 700 g/t).
Fenitised peralkaline granites and agpaitic pegmatites of the Amis complex contain Y-fluorite, monazite, xenotime, bastnaesite and fergusonite. The Amis Complex represents a late intrusive phase associated with the Brandberg anorogenic granite intrusion.
It consists of peralkaline, arfvedsonite-bearing granitic and pegmatitic dikes and sills and is characterized by locally extreme enrichments in REE and rare metals with high charge-ionic radius ratios, such as Zr and Nb.
The highest concentrations (e.g., 1.7 wt % Zr, 0.3 wt % Nb, 0.5 wt % total REE) are found in aegirine-albite aplites that formed around arfvedsonite pegmatite cores.
Thorium, yttrium and rare earth element occurrences associated with placer deposits
Toscanini monazite occurrence
A monazite-bearing marine placer deposit was found in the Skeleton Coast Park near Toscanini. The monazite-bearing sands occur along a coastal strip some 22 km long, stretching from about 31 km south of Torra Bay to 20o 40’ south.
The extent of the deposit is outlined by a prominent radiogenic anomaly. The bedrock consists of quartz latites of the Etendeka Formation and sediments of the Toscanini Formation. The source of the monazite is unknown, but it can be speculated that it is possibly derived from Pan African granites that occur south of the deposit.
The monazite was presumably transported in a northerly direction by the Benguela current and subsequently concentrated and deposited by marine processes.
Rare earth element mineralization in South Africa occurs in heavy mineral sand deposits, in pegmatites and granites of the Namaqualand Metamorpic Complex, in carbonatites and alkaline complexes and in the fluorite-bearing rocks associated with the Bushveld Igneous Complex.
South Africa’s known and demonstrated recoverable reserves were estimated in 1988 at 2.187 million metric tons of REO in two deposits; placer monazite at Richards Bay and rare earth bearing apatite at the Phalaborwa Complex (Van der Vyver, G P: Resources of Rare Earths in South Africa, Minerals Bureau, 1988).
These reserves, at the time, placed South Africa third in the world after China and the USA, but South Africa never developed a rare earth mining and refining industry. The other known occurrences in South Africa have not been adequately explored to be classified as demonstrated resources.
Although South Africa produced rare earth-bearing monazite concentrates at Richards Bay Minerals (RBM), production stopped before 2003 and RBM, like Ticor and Namakwa Sands, currently recovers only ilmenite, rutile and zircon.
The rare earth-bearing apatite concentrates of Phalaborwa have been investigated by MINTEK repeatedly with the view of producing rare earth oxides.
The Steenkampskraal monazite mine at Van Rynsdorp in Namaqualand, operated from 1952 to 1963, producing a monazite concentrate that was sold mostly for its thorium content rather than its rare earth content. It was the largest thorium source in the world during the years 1951 to 1963.
Richards Bay Minerals
Placer-type deposit with monazite plus thorium and consequently with a radioactive hazard problem.
Richards bay Minerals (RBM), jointly owned by Billiton and Rio Tinto, is the largest single producer of titanium in the world from heavy mineral deposits. RBM now accounts for about 25% of world output of titanium feedstocks (titania slag and rutile), 33% of world zircon output and 25% of high purity pig iron. The sand deposits contain REE-bearing monazite and the recoverable resource was estimated at 27,500 tonnes REO in 1988.
Phalaborwa Complex
Carbonatite-type deposit with a low-grade, high tonnage potential
The Phalaborwa Complex is a zoned pyroxenite-syenite-carbonatite intrusion located on four farms in Mpumalanga Province. It hosts South Africa’s largest copper mine and produces, in addition, magnetite, sulphuric acid, zirconia, uranium, precious metals, vermiculite (Rio Tinto) and phosphate (FOSKOR).
The REE occur mainly in the phosphate mineral apatite and the P2O5 content varies from 6% to 8% within the pyroxenites and the foskorite (altered magnetite-olivine-apatite carbonatite). Rio Tnto’s Palabora Mining Company has a standing contractual arrangement whereby the apatite concentrates are delivered to FOSKOR for the production of phosphate in exchange for copper concentrates from FOSKOR. The apatite concentrate contains on average 0.5% rare earth oxides. The total recoverable resource has been estimated at 2,160, 000 tonnes REO.
The europium content is in excess of 1% in the rare earth concentrates and the thorium oxide content of the rare earth concentrates is below 200 ppm. FOSKOR’s associated company, Sentrachem, conducted various investigations and tests by MINTEK on the concentrates with the view of recovering the individual rare earths.
Steenkampskraal monazite mine
Pegmatite-type deposit with low tonnage potential
The Steenkampskraal monazite deposit occurs in a sequence of highly metamorphosed crystalline gneisses of the Roodewal Suite of the Namaqualand Metamorphic Complex.
The rocks are the host in which the pegmatite ore body occurs. The monazite-bearing ore body is tabular in shape with an undulating form and a thickness varying from 30 cm to 90 cm.
Minerals present in the ore body include monazite, quartz, apatite and magnetite with small amounts of zircon, pyrite, chalcopyrite, galena and ilmenite. The monazite is the source of the rare earths. The average in situ grade is 16.74% REO, 0.8% Cu, 0.5g/t Au and 6.0g/t Ag. The estimated reserve is 20 00 tonnes REO.
Great Western Minerals Group Ltd (Canadian) has an option to explore, develop and eventually buy the total production from Rare Earth Extraction Company Ltd. The developer of the South Africa-based Steenkampskraal rare-earths project, TSX-V-listed Great Western Metals Group (GWMG) said in May 2012 it had filed a Canadian National Instrument 43-101-compliant resource report with Canadian Securities Administrators.
The report states that Steenkampskraal hosted a resource of 131 500 t of rare-earth minerals in the indicated and inferred categories, with about 37 500 t of resources located in the upper and lower tailings dams.
GWMG said it had notified its escrow agent that it had satisfied the escrow release condition of the $90-million convertible bond financing and expects the remaining $10.8-million, earmarked to satisfy interest payments, to be released to the company in due course.
In order to satisfy the escrow release condition, GWMG had to confirm that at least 20 000 t of total rare-earth oxides (TREO) including yttrium, in the sum of the measured, indicated, and inferred resource categories are present at the Steenkampskraal property using a 1% cut-off grade.
The NI 43-101 report pointed to the presence of 13 823.64 t of TREO including yttrium under the indicated resource category and 14 147.76 t under the inferred resource category.
The aspiring integrated rare-earths producer on Wednesday said it had narrowed its first-quarter loss to $3.06-million when compared with the loss of $4.86-million in the same period a year ago.
Other carbonatites and alkaline complexes with rare earth element mineralization.
Mineralized carbonatites usually contain a high concentration of the so-called light rare earth elements lanthanum, cerium, neodymium, praseodymium and samaruim. The minerals containing the rare earths occur dispersed in the calcite (Ca-rich), and, dolomite (Mg-rich) and ankerite (Fe-rich) forming the bulk of the carbonatite.
If a carbonatite or complex consists of multiple intrusions or phases, the rare earth element content tends to increase in the youngest phases. Apatite is considered to be an accessory phase of carbonatites and contains substantial rare earth elements remobilised by hydrothermal fluids.
The rare earth minerals bastnaesite, parisite and synchisite are considered to be supergene, i. e. formed at shallow depth by the action of groundwater. (Mountain Pass in California and Mt Weld in Australia, where the ore-grade mineralization occurs between 30 metres and 60 metres below the present-day surface, are examples where the supergene enriched portions of the carbonatites are of economic interest).
The Glenover Carbonatite Complex
The Glenover Carbonatite Complex, 80km north-northwest of Thabazimbi, comprises an oval shaped, poorly exposed pyroxenite and carbonatite body, 4.7 km long and 3.5 km wide. Monazite is bound in a coarse-grained sövite (Ca-rich) and magnesio-carbonatite.
Associated minerals include apatite, magnetite, phlogopite and pyrochlore. Associated secondary minerals include quartz, synchisite, fluorite, barite, monazite and columbite. The presence of synchisite could indicate supergene enrichment in rare earth mineralization of the brecciated complex, but there is no information available on the distribution of the rare earth minerals.
The Kruidfontein Complex
The Kruidfontein Complex is situated approximately 130km north-northwest of Pretoria. It has a caldera structure, along a NW-striking regional fault. The carbonatites represent the last stage of extrusive activity of the Kruidfontein Complex.
Rare earths associated with fluorite (CaF2) mineralization occur associated with the intrusive (fluorite-rich dykes and plugs) and extrusive (replacement and disseminated ore) carbonatitic rocks.
A large tabular stratiform ore body occurs in the southwestern part of the Complex, and contains an average of 30% CaF2. Fluorite occurs disseminated throughout the inner zone with concentrations not exceeding 10% CaF2. Analytical results from the inner zone show that the fluorite contains La2O3 in variable concentrations between 0.02 and 0.15 wt%.
The Pilanesberg Complex
Rare earths are found in alkaline rocks of Pilanesberg on Thabayadiotsa on the farms Houwater 54, Rhenosterspruit 59 and Saulspoort 38.
Rare earth mineralization on Houwater 54 occurs as veins in the contact zone between a tinguaite ring dyke and younger foyaite, On the farm Rhenosterspruit 59, rare earth mineralization occurs in tuff bands intercalated with lava over a distance of 2 km. On the farm Saulspoort 38, rare earth mineralization occurs as veins in a white foyaite. Yttrium and REE are concentrated in britholite ((Ce,Ca,Th,La,Nd)5(SiO4,PO4)3(OH,F) ) veins and britholite-bearing foyaite.
High grade mineralization consists of britholite containining 56.36% REO and 1.56% ThO2 and magnetite with minor amounts of allanite, apatite, calcite, strontianite, fluorite, aegirine and cheralite.
The reserves have been estimated at 13.5 Mt at 0.7% REO +ThO2, 1.2 Mt at 6.54% REO +ThO2, and 24 000t at 10% REO+ThO2.
The Vergenoeg magnetite-fluorite deposit
The Vergenoeg breccia pipe is located in Gauteng Province approximately 80 kilometers northeast of Pretoria. Vergenoeg is a fluorite-bearing massive iron oxide deposit that is genetically related to granites of the Bushveld Complex.
The deposit is a funnel-shaped breccia pipe, with a diameter of 900 m (north-northwest) to 700 m (east-northeast) on surface, which contains fluorite, apatite, ilmenite and magnetite.
Vergenoeg is a fluorite mine, despite the large volumes of magnetite and has produced fluorite since 1956. The fluorite ore body, up to a depth of 360 m has a resource estimate of 174 Mt at 28.1% CaF2. The iron resource is in the order of 195 Mt at 42% Fe.
Mining has been focused on the upper part of the pipe-shaped body (porous botryoidal hematite-goethite gossan). The gossan contains resistant minerals such as cassiterite, apatite and rare earth carbonates.
Siderite is often found with the REE minerals, normally occurring in veinlets and coarse-grained masses. REE minerals in the upper part of the pipe may have originated from remobilization of allanite from the lower part of the pipe.
Similarly remobilization might have resulted in the REE mineralization seen in the siderite veins and interstitial grains between apatite laths, including monazite.
The primary assemblage of minerals in the lower part of the Vergenoeg pipe comprises mainly of fluorite, ilmenite and fayalite (Fe2SiO4) with minor pyrrhotite, apatite and allanite.
Allanite is the most common REE-bearing mineral in the primary mineral assemblage and are intergrown with fayalite and ilmenite.
It seems that the REE potential of Vergenoeg has not been investigated systematically and no further information on the distribution and grade of the REE mineralization could be obtained.
Similarities with Phalaborwa and also with Bayan Obo, Mongolia, indicate that the Vergenoeg pegmatoid pipe could be an extreme carbonatite-associated member of the Fe-oxide Cu–Au (±REE±P) group of deposits. (Goff, B. H., Weinberg, R, Groves, D. I.; Vielreicher, N. M.; Fourie, P. J.: The giant Vergenoeg fluorite deposit in a magnetite–fluorite–fayalite REE pipe: a hydrothermally-altered carbonatite-related pegmatoid?; Mineralogy and Petrology, Volume 80, Numbers 3-4, March 2004 , pp. 173-199).
Metorex sold its 55% shareholding in Vergenoeg to its Spanish partner, Minerales y Productos Derivados S.A. (“Minersa”) in December 2009 for US$60 m. (Metorex acquired the mine in 1999 when its former owner - chemical giant Bayer - decided to sell out as part of its drive to dispose of non-core operations and concentrate on its main business - the manufacture of chemicals.
Metorex then promptly sold 30% of Vergenoeg to the Spanish chemical group Minersa, which also bought a 20% direct stake in Metorex itself, becoming one of the group's largest shareholders).
The Buffalo Fluorspar Deposit
The deposit is situated about 75 km north of Vergenoeg near Mookgopong (formerly Naboomspruit) in Limpopo Province and contains fluorite veins which cut through altered rhyolite of the Rooiberg Group, which is surrounded by the Bushveld Complex granite.
Buffalo fluorite mine was mothballed in October 2008 due to market circumstances. Ongoing empirical test work to reduce the phosphorous content of its product was in progress.
In addition, test work on the fines from the substantial aggregate dumps on the neighbouring property continued. If either of these projects are revived and proves successful, Buffalo could be re-opened.
One of the opportunities at Buffalo that Sallies Ltd, the previous owner, planned to investigate further was the rare earth minerals contained within tailings.
During 2009 Firebird Global Master Fund, Ltd (Incorporated in the Cayman Islands) made a successful offer for the shares that they did not already owned.
The Zandkops Drift Complex
The pipe-like vermiculite-calcite-limonite body, similar in character to deeply weathered complexes like Mount Weld in Australia, is located approximately 26 km southwest of Garies, in the Northern Cape.
Pyrochlore and secondary REE mineralization is associated with manganoan calcite, goyazite, gorceixite, carbonate-apatite, betafite, uraninite, and niobium rutile.
A bulk sample assayed 2.6% P2O5, 900 ppm Nb, 0.069 kg/t U3O8, 0.197 kg/t ThO2, 1.2 %REO+ThO2 and 320 ppm Mo, but beneficiation tests yielded disappointing results.
The cost "curve" for uranium is more like a hockey stick. We have a good deal of low-cost production in the world, which can be extracted for $10 to $15 per pound. Much of this comes from Saskatchewan, where high-grade ore makes for lower costs.
