Friday, February 17, 2017

Montepuez ruby mine, Mozambique

The Montepuez ruby deposit is located in the northeast of Mozambique. Covering 33,600 hectares, it is the most significant recently discovered ruby deposit in the world.

The concession is located at a geologically critical junction between the north-south trending Mozambique Belt and the east-west trending Zambezi Belt. Both are “treasure-bearing” Neoproterozoic orogenic belts within the global Pan-African tectonic framework.

Estimates of probable ore reserves are 432 million carats at a diluted grade of 15.7 carats per tonne.
Gemfields PlC (LON:GEM) announced last year that Montepuez has enough reserves to last 21 years. Rubies are formed when fluid derived from the parental magma interacted with the host rocks under a silica unsaturated environment. After hundreds of millions years of erosion, rubies are liberated from the host rock and transported and concentrated by water and eventually settled in alluvial, colluvial, and eluvial deposits.
At its inaugural June 2014 auction of ruby and corundum Montepuez ruby achieved $33.5 million or an average $18.43 per carat with 92 percent sold by lot.

The auction saw 2.03 million carats of ruby and corundum placed on offer, of which 1.82 million carats were sold.

If this is the case, the stone could yield a cut and polished ruby with a wholesale value of $1.5 million or more.
In November 2015 Gemfields discovered a 40.23-carat ruby at Montepuez which it has called “one of the most important rubies unearthed in recent times”

While the yield from the rough varies, one may assume 30 to 40 percent. This should provide a 12 to 16 carat gem. The question is how clean the stone is and if it requires heat treatment. A clean stone without heat treatment is more valuable.
The stone is significant because it attests to the mine’s ability to produce important rubies.

Due to the rarity of rubies, the discovery of a 40-carat ruby is comparable to finding a 100-carat rough diamond.