Friday, August 19, 2016

Montepuez ruby deposit, Mozambique

The Montepuez ruby deposit is located in the northeast of Mozambique in the Cabo Delgado province.

Covering approximately 33,600 hectares, it is the most significant recently discovered ruby deposit in the world.

Estimates of probable ore reserves are 432 million carats at a diluted grade of 15.7 carats per tonne over 21 years.
Precious stones miner Gemfields (LON:GEM) announced that an independent report has confirmed Montepuez has enough reserves to last at least 20 years.

According to the report the mine's indicated and inferred mineral resource stand at 467 million carats of ruby and corundum at a grade of 62.3 carats per tonne.

Gemfields' Rhino anti-poaching plane.
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 (approximately 800–500 million years old) orogenic belts within the global Pan-African tectonic framework.
Primary 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.
Gemfields Plc reported that its inaugural June 2014 auction of ruby and corundum from Montepuez achieved $33.5 million or an average $18.43 per carat.

The auction was 92 percent sold by lot.
In November 2014 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 depends the shape, inclusions, and the nature of the crystal, “one may assume yield of 30 percent to 40 percent. This should provide you with a 12 to 16 carat gem.”
The important question would be how clean the stone is and whether or not it requires heat treatment. A clean stone without heat treatment is far more valuable.

In this case, the piece of rough could yield a cut and polished ruby with a wholesale value of $1.5 million or more.
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. In 2015 Gemfields uncovered a very rare pair of matching rubies which total 45 carats.