A marble-hosted wollastonite deposit at Bi’r Ash Shumt, Kingdom of Saudi Arabia

Abstract EN

Wollastonite is an acicular calcium silicate used by the ceramics industry for glaz- ing and by the plastics industry as reinforcing agent for polymeres.

The Bi'r Ash Shumt wollastonite deposit was discovered by BRGM for the DMMR in Pre- cambrian Hulayfah group mainly volcanic Afna formation rocks (andesite and rhyolite).

De- tailed geologic investigations in I9S7, characterized this deposit as produced by contact metamorphism on marbles in a structural context favourable for silica percolation.

Geometric relationships with an intrusive body of post-Hulayfah amphibolc granodiorite are no longer observable.

The metamorphic assemblage comprises garnet, wollastonite.

vesuvianite.

epi- dote and diopside.

by order of appearance in the marble.

Surface sampling and mapping were accompanied by a new procedure for resource estima- tion.

using chemical analysis, normative calculations, and semiquantitative petrographic examination.

Wollastonite grades estimated quantitatively from petrographic samples range between 35 and 60%.

averaging 50%.

Grades evaluated from geochemical rock samples range between 20 and 50%.

averaging 34%.

Garnet-vesuvianite epitaxic crystal intergrowths are the second constituent (15-30% of rock volume), followed by calcite and diopside.

A beneficiation process was developed in view of the specific constraints of the Kingdom, with an on-site mechanical preparation and dry magnetic separation of garnet.

A wet leaching procedure by injection of SO: reduces the calcite amount, followed by a magnetic separation of the released impurities.

Inferred resources of 500,000 tons of wollastonite arc estimated.

Further improvements to the beneficiation process arc needed for a final assessment of the po- tential of the deposit, along with a volume evaluation through drilling.