New Mexico Mineral Symposium — Abstracts

Broken Hill, in the state of New South Wales, Australia, is not merely one of the world's largest deposits of silver, lead, and zinc. It is also one of the greatest sources of mineral specimens ever known. Over 100 years of continuous mining operations have produced a suite of mineral specimens ranging from the unique to the spectacular. Unfortunately, the great majority of these went to the smelters and only a relatively small percentage has found its way into collections.

The mines of Broken Hill have contributed significantly to mining and ore treatment technolo-gies and have helped make Australia one of the world's leading producers of silver, lead, and zinc for decades. They led to the formation of companies that played a leading role in developing Australia's industry and economy. One of these was BHP (Broken Hill Proprietary), which is now an industrial giant with interests in steel, manufacturing, coal, oil, gas and minerals both in Australia nd overseas. It is very unlikely that any single mining district of the future will exert as much influence on Australian life as Broken Hill.

Until recently, there has been much controversy over the formation of the Broken hill orebody. It is now accepted that it is a metamorphosed stratiform volcanic exhalation deposit originally formed about 1.8 billion years ago. Since that time there have been several events of heavy deformation and metamorphosis as well as a series of granitic and doleritic intrusions. In the past 20 million years, the orebody was uplifted to form the Barrier Range, and erosion and oxidation began. The current lode is shaped like an inverted boomerang and is about 5 mi long, 3,000 ft deep, and about 1,500 ft wide. It has been oxidized to a depth from 300 to 600 ft. The episodes of metamorphosis, the oxidation, together with the fact that the primary ore was rich in copper, calcium, manganese, bismuth, cobalt, nickel, phosphorus, fluorine, chlorine, bromine, and iodine (besides silver, lead, and zinc), have led to the formation of unique and spectacular suites of minerals in the main lode and surrounding area. Reports from the early days show that miners were amazed by the discovery of hundreds of vugs, some the size of rooms, covered with magnificent crystals and stalactites of anglesite, cerussite, smithsonite, azurite, malachite, coronadite, silver halides, pyromorphite, native silver and copper, as well as many other rare secondary minerals. Unfortunately, most were not preserved and went to the smelters. The relatively small number that were preserved are eagerly sought by collectors and museums alike, and several are among the world's best for the species. To date, over 250 distinct species have been identified from the main lode alone, and over 430 from the mines in a 30-mi radius of the main lode. Broken Hill is the type locality for 10 species; this list is likely to increase with recent systematic collecting and studies of specimens from the backfill of the old stopes and with recent mining of the remnants of the oxidized zone in the Kintore and Block 14 opencuts near the center of the lode. In the last few years, these studies have uncovered over 50 rare species previously unrecorded from Broken Hill including several rare phosphates, arsenates, and sulphates that appear to be new to science. These studies should shed additional light on the origins and paragenesis of this complex deposit.