Serra Verde lateritic REE deposit

We are developing a formation model for the Serra Verde deposit in the Goiás province of central Brazil, to investigate its potential for rare earth elements (REE) extraction. 

The Serra Verde deposit is rich in recoverable REE, with an inferred resource of 458 million metric tonnes at a grade of 0.098 per cent total REE (May 2012, 43-101 compliant). Heavy rare earth elements (HREE) account for 24 per cent of the deposit.

The REE typically occur in a six metre-deep layer of clay-bearing saprolite produced by the deep weathering of granite. Initial testing suggests that more than 50 per cent of the REE bulk is sorbed on clay and can be recovered by a simple elution process.

The Serra Verde project will develop a model for the introduction, enrichment and mineralogical residence of REE at the Serra Verde deposit. We aim to: 

• establish links between multiple magmatic events and REE introduction
• determine and quantify the processes leading to REE enrichment
• assess the effect of tropical weathering on REE grades and distribution
• identify the residence of REE in primary, secondary and supergene minerals

Serra Verde Mining is supporting a PhD project undertaken by Carmen Pinto-Ward and co-hosted by the Museum and Imperial College London. Email Carmen for further details.

Deposit formation

The Serra Verde REE deposit is associated with a Proterozoic alkali granite within the Goiás province  of Brazil. The REE introduction and enrichment may be related to three main stages of geological evolution: 

• Emplacement of the Pela Ema tin granites (~1.8 Ga). This resulted in the formation of typical tin-bearing greisen veins hosting monazite and xenotime.
• Intrusion of an evolved alkaline (possibly carbonatite) complex at depth (~540 Ma).This caused potassium metasomatism (K-feldspar-biotite) with additional introduction or recrystallisation of monazite, xenotime and magnetite.
• Lateritisation, possibly during the Miocene. 

A 30-35 metre thick lateritic weathering profile developed, resulting in the breakdown of feldspars to clay and the dissolution of REE-bearing minerals with reprecipitation in the saprolite ore zone. Colluvial accumulations of REE are also present.