Exploration and Mining Development for Hard Minerals in the Australian Coastal Zone

Abstract

ABSTRACT This paper reviews recent exploration and mining developments for hard minerals in the Australian Coastal Zone. The review provides details of recent exploration and mining developments for shellsand off South West Western Australia, diamond exploration in Northern Western Australia, heavy mineral exploration offshore off South Eastern Australia and research into proposed construction sand mining offshore off Sydney. These projects have led to improvements in resource assessment, mining techniques and environmental management, with broad application for mining developments in the coastal zone worldwide. INTRODUCTION There has been considerable interest in the development of hard minerals in the Australian Coastal Zone in recent years. These minerals include diamonds, rutile, zircon, ilmenite, lime sands, coral and construction sand. At the same time, reduced availability of onshore sources, changes in regulatory requirements and environmental expectations has demanded establishment of better ways to define resources, predict environmental impacts, mine, monitor and manage offshore developments. As a result, some significant progress has been made, particularly in understanding mineral occurrences and managing environmental impacts. Specific cases are presented, detailing developments in a range of mineral commodities and coastal environments for diamond exploration in North Western Australia, heavy mineral exploration off South Eastern Australia, shellsand mining and environmental research in South West, Western Australia and environmental research into proposed mining of construction sand off South Eastern Australia. The location of these sites is shown in Figure I. WESTERN AUSTRALIA 1. Shellsand Mining, Fremantle Cockburn Cement Limited has dredged shellsands from calcareous sand banks offshore off Fremantle since 1972,(Figure 1). The shellsands comprise deposits of surficial unconsolidated sands with a calcium carbonate content of 92%. The shellsands provide feedstock for the largest lime manufacturing works in Australia and one of the largest in the world, being a major supplier to the region's mineral processing industry. The shellsands are also usedin the manufacture of cement. The Western Australian Legislation provides for exclusive extraction rights to 2011. Under the legislation since 1986, Cockburn Cement is required to submit a Dredgingand Management Programme every two years (I), outlining the planned dredging and management activities for the operation covering the ensuing 10 year period. The shellsand deposits contain resources to support production requirements of 1-2 million tonnes per year. The resource is located in submarine sand shoals lying in water depths of 2-15m. The shellsand deposits lie 8 km off the coast, which typically comprises sandy beaches, limestone rocky shores and headlands. The dredge site is located some 6.5km from Fremantle. The shellsand deposits developed over the period 1,000-4,000 years BP, as a result of fluctuating sea level which allowed transportation and deposition of mobile sand to accumulate in basins. This amounted for some 42% of the present deposits, with the remainder being generated through biogenic production of carbonate secreting organisms. Such material can generate at up to 2.2kg/m2/year. Mining of the shellsand deposits is undertaken using a water jet suction dredge, operating at 800 tonnes per hour in water depths between 5-15m. The dredge sand is transferred to split hopper barges for transportation to a shore based reclaimer.