Overview

Superior is exploring for copper, lead, zinc, silver and gold in north Queensland. The principal target types are Mount Isa style copper and lead-zinc-silver deposits in northwest Queensland, volcanogenic massive sulphide (VMS) and porphyry copper style copper-gold deposits in northeast Queensland and high-grade gold deposits at Tick Hill in northwest Queensland.

Mount Isa Style Copper and Lead-Zinc-Silver Deposits

The north-west Queensland area has been a major producer of copper, lead, zinc and silver. It ranks as one of the world's great mineral provinces. Major production currently comes from Mount Isa (copper, lead, zinc and silver), Cannington (lead, zinc and silver), Century (lead, zinc and silver) and Ernest Henry (copper and gold). A number of smaller mines are also in production.

The northwest Queensland area has considerable potential for the discovery of additional copper and lead-zinc-silver deposits.

Base Metal Model - Click to Enlarge Some large Proterozoic copper and lead-zinc-silver deposits are thought to have formed at or near the ground surface within fine-grained sediments adjacent to large fault zones which existed at the time of sediment deposition. Hot hypersaline solutions, probably derived from buried evaporitic sediments, are thought to have leached metals from sub-surface rocks and to have carried them to the near surface environment where they have formed metal sulphide deposits. Rocks that were enriched in metals were probably important as source rocks for metal deposits. For example, basalt, which contains an appreciable copper content, was probably an important source rock for copper in deposits.

Mount Isa Sections - Click to Enlarge Superior's has adopted a conceptual approach in the search for large Proterozoic deposits in north-west Queensland. This has involved identifying favourable geological settings which are believed to be prospective for copper and lead-zinc-silver deposits based on a knowledge of the existing deposits and the regional geology. Greater attention has been given to the characteristics of the Mount Isa copper and lead-zinc-silver deposits in determining favourable geological settings for deposits.

Regional geophysical surveys, particularly airborne magnetics, have allowed the regional geology to be interpreted in shallow covered areas beyond the outcropping areas where reasonable geological maps exist. This has considerably expanded the prospective search area.

The primary aim of Superior's exploration program is to discover a major Mount Isa style copper deposit. The secondary aim is to find a major lead-zinc-silver deposit of the Mount Isa style.

The principal components of the Proterozoic copper exploration model being used by Superior in the Mount Isa Inlier are:

  • Thick sequences of metamorphosed basic volcanics (basalts) as a source of copper for deposit formation. Basic volcanics commonly show as magnetically active areas in airborne magnetic surveys and this allows them to be readily identified in covered areas.
  • Evidence for the operation of large Proterozoic hydrothermal cells within the basic volcanic sequences to leach and then transport the copper to depositional sites. Hydrothermal activity results in the destruction of magnetic minerals within the basic volcanics and evidence of the action of hydrothermal cells may show in airborne magnetic surveys where localized areas of magnetite destruction exist.
  • Thick sequences of fine-grained sediments which overlie the basic volcanic sequences and which act as depositional sites during deposit formation. In the Mount Isa area, sediments typically show as quiet areas in airborne magnetic surveys and these also can be readily identified in covered areas.
  • Presence of growth faults that were active at the time of sediment deposition and which potentially acted as conduits to focus fluid flow to depositional sites. Faults which juxtapose the potential basic volcanics copper source rocks against the depositional sediments are preferable.
  • The presence of extensive iron (pyrite) mineralisation which can be associated with copper and lead-zinc-silver mineralisation.
  • The presence of stratiform lead-zinc-silver mineralization which may be associated with copper mineralization.
  • The presence of veins and lodes of copper, lead and zinc which might indicate ‘leakage’ from a larger deposit. This also includes ‘leakage’ into overlying later sedimentary formations such as the Cambrian carbonate bearing sequences in and around the Mount Isa Inlier.

Volcanogenic Massive Sulphide Deposits

Volcanogenic massive sulphide (VMS) deposits are a type of metal sulphide deposit representing a significant source of the world’s copper, lead, zinc, silver and gold. They were formed on or close to the sea floor during volcanic-associated hydrothermal events in submarine environments (black smokers). The deposits were often layered accumulations of sulphide minerals on the sea floor which became interbedded with the enclosing sediments and were subjected to later deformation and metamorphism during tectonic events.

The Balcooma, Reward and Thalanga deposits in the northeast Queensland area are VMS deposits which occur in rocks of similar age to those that are being explored by Superior.

As mineral exploration has extended into more remote areas it has become more difficult to find prospects of the VMS type with outcropping gossans after sulphides and exploration now largely depends on drilling of geophysical and other targets.

One of the features of these deposits is that the valuable metal sulphides in the deposits are often associated with adjacent barren or poorly mineralised pyrite accumulations.

A further feature of VMS deposits is that they often are multi-element deposits with high metal grades and the value of the ores is often high.

Tick Hill Type High-Grade Gold Deposits

The Tick Hill gold deposit is an unusual high-grade gold deposit which was mined between 1991 and 1995 by Carpentaria Gold Pty Ltd (a subsidiary of MIM Holdings Limited) for the production of 513,333 ounces of gold from 705,000 tonnes of ore at a recovered grade of 22.6 g/t gold (MIM Holdings Limited – Annual Reports).

The high-grade of the Tick Hill deposit makes exploration for this style of deposit attractive and the best place to explore for deposits of this style is adjacent to existing deposits.