Gold

By Leia Michele Toovey-Exclusive to Gold Investing News

Greenstone belts host economical deposits of many minerals including gold, silver, copper, and zinc. Gold is found in Achaean age greenstone belts in Australia, southern Africa and Canada. While greenstone belts host a variety of minerals, gold is most commonly found along the edges of these belts and associated with structural features.

The minerals in the metamorphic rocks that make up greenstone belts are , as the name suggests, green in color. The term appears often in mining literature because greenstone belts are extremely common, and are found on almost every continent.

Greenstone belts can be found in association with cratons—the older, stable part of continents that have survived many cycles of merging and rifting. The craton is generally found towards the interior of tectonic plates. Because greenstone belts have survived many cycles of tectonics, their stratigraphy is complex.  Greenstone belts contain a great number of individual rock units. Generally speaking, greenstone belts are composed of volcanic rocks that also have small amounts of sedimentary rocks interwoven within the various volcanic rocks. One of the most common rocks associated with greenstone belts is conglomerate. Conglomerates are often gold-bearing. A prime example of a gold-bearing conglomerate is the Abitibi Greenstone Belt in Canada. Greenstone belts vary dramatically in size, ranging from as little as several dozen to several thousand kilometers in length.

Geologists have come up with two contrasting models to explain the formation of greenstone belts. One side of the camp believes that the magmatic and tectonic processes during formation of greenstone belts in Archean times were different to present-day plate tectonics. They cite differences in mineralogy and point out that there are no modern analogues to greenstone belts as supporting evidence. The other side believes that greenstones may have formed in volcanic arcs or inter-arc or back-arc basins. These geologists interpret greenstone belts as collages of oceanic crust, island arcs and accretionary prisms.  For support, this side of the argument has  recent experimental work on the origin of komatiitic magmas, which have extremely high melting points and are the magmas that are associated with greenstone belts. The experimental work on komatiitic magma shows that the
temperatures required for their formation indicate that the Archean upper mantle was not significantly hotter than today.

An example of a Greenstone Belt: The Abitibi

The Abitibi Greenstone Belt is one of the largest greenstone belts in the world. Spanning the Ontario-Quebec border, exploration is still underway on this deposit, which has already proven to host significant deposits of gold. To date, the Abitibi Greenstone Belt has generated over 160 million ounces of gold.

The Yilgarn Craton, Australia

The Yilgarn Craton, Australia’s premier mineral province, garners more than half of Australia’s minerals exploration expenditure while accounting for two thirds of all gold production and most of the nickel produced in Australia. The craton contains approximately 30 percent of the world’s known gold reserves, about 20 percent of the world’s nickel reserves and 80 percent of the world’s tantalum reserves; it  also hosts considerable deposits of iron, zinc and copper. Mining in the Yilgarn Craton is conducted mostly in the greenstone belts.

A sample of miners and explorers

Catalina Metals Corp. (CVE:CTX.H)

This March, Catalina signed an agreement, subject to regulatory acceptance, to acquire 18,000 contiguous acres of prospective gold property in the Rainy River greenstone belt in Ontario. The property lies along a major inflection in the greenstone belt and is host to the same geological and structural controls that host the Rainy River and Cameron Lake deposits as well as numerous other gold and base metal occurrences in the district.

North Country Gold Corp. (CVE:NCG)

North Country Gold holds 100 percent interest in approximately 567,000 acres of land along a greenstone belt in Nunavut. Included is the Three Bluffs high-grade Gold deposit with a NI 43-101 compliant deposit estimate of 2.7 Mt at 5.85 g/t gold for 508,000 oz. gold (indicated) and 1.27 Mt at 5.98 g/t gold for 244,600 oz. gold (inferred), open to depth and along strike there is significant potential to expand the current resource.

Indigo Exploration Inc.(CVE:IXI)

Indigo Exploration holds four gold exploration permits and has a fifth permit under option in Burkina Faso, West Africa. These projects lie within the Birimian Greenstone Belt of West Africa, one of the most prolific gold producing regions of the world.

Centerra Gold (TSE:CG)

Centerra is a gold company focused on acquiring, exploring, developing and operating gold properties primarily in Asia, the former Soviet Union and other emerging markets worldwide. Centerra is a leading North American-based gold producer and the largest Western-based gold producer in Central Asia and the former Soviet Union.