Coastal Sand Mining – Background
Southeastern Australia has been endowed (some would say cursed) with concentrations of a group of heavy minerals in coastal sand deposits. The geological history and geomorphological emplacement of these heavy minerals has influenced the professional lives of many. It is a history rich in discoveries, conflict, drama, frustration and lots of intellectual satisfaction.
In 1960 I was introduced to Peter McKenzie, a BHP geologist, surfing champion, keen observer of coastal processes, and a former employee of a sand mining company. He was a great mentor to me. I met some of his sand mining colleagues who freely shared stratigraphic information on areas of interest. It was a taste of things to come because on returning to Australia in the 70s I resumed contact. It was a period of extensive drilling and exposure of deposits from Wyong to Fraser Island. In this way sand mining helped me understand the Quaternary coastal evolution in SE Australia.
What are heavy minerals, what is their origin and how did they get into coastal sand deposits? Many have addressed these question; this is a very cut down version. We are dealing with minerals that have a specific gravity roughly double that of quartz, the dominant coastal sand mineral. This allows for wave and wind processes to selectively concentrate these minerals. Rutile, zircon and ilmenite are the three dominant heavy minerals of commercial value, and they occur within silicious (quartz) sands as “placer” and aeolian deposits along the east coast of Late Quaternary age; however along southern and western coasts they are in deposits of Tertiary (or early Quaternary) age landward of carbonate sands and limestones (see recent study of such deposits to the rear of the Nullabor Plain (Eucla Basin) in South Australia by B. Hou et al., Geological Survey of South Australia Report 2022/00011).
Over the years there has been much debate on the age and source of the heavy minerals found along the east coast. John Veevers has reviewed the literature and offered new evidence based on radiometric dating of zircon ( Veevers, J., 2015, Australian Journal of Earth Sciences, 62, 385-408). These sand grains are resistant to weathering so survive today on our beaches. Veevers concluded that they can be traced through several cycles of formation, erosion, deposition and recycling to the present. In his words: “The properties of the 700-500 million years primary zircons are traceable through first cycle Ordovician turbidite and intruding second-cycle granite and younger sediment, such as the third cycle Hawkesbury Sandstone”.
Now to the drama. East coast sand mining once contributed a large part of the world’s supply of zircon and rutile as far back as 1936. But during World War 2 atomic energy became a matter of concern to governments. The heavy mineral suite includes a minor amount of monazite, a source of cerium and of thorium, a fissionable element that at this time was seen as a potential source of atomic power. The Australian Government tasked the Bureau of Mineral Resources (BMR) to study the distribution and reserves of what was then termed “beach-sand deposits” between Southport in southern Queensland and the Clarence River with the primary object to determine the reserves of monazite and hence thorium. As a corollary they could also determine reserves of zircon, ilmenite and rutile. BMR started this work in July 1947, finishing field work in December 1950 and publishing the result in 1955. BMR Bulletin No. 28 is a remarkable study authored D. E. Gardner: “Beach-sand heavy mineral deposits of Eastern Australia” (1955). I treasure my copy, much annotated and used as part of an initial visit to many of the sites in 1961. It was clear by the end of this work that monazite was not going to underpin Australian atomic program, but those other three heavy minerals would otherwise enrich us!
Gardner’s investigations stand out as the first comprehensive study of modes of deposition, distribution and immediate subsurface stratigraphy of east coast heavy mineral deposits. Even today we can be amazed at the detail on his maps and sections. He introduced the term “transgressive dune” and understood age implications of induration with carbon-rich material. I struggled at times with his interpretations of sea level change. However, he offered a foundation for many of us who were then researching Quaternary coastal evolution.
In 1971 I was introduced to a young geologist in the NSW Geological Survey, Peter Roy. At that time he was investigating heavy minerals in estuaries. The NSW Government wanted the Geological Survey, not individual mining companies, to determine whether there were commercial quantities of heavy mineral sand in estuaries such as Tuggerah Lakes. This was the beginning of an incredible career as the NSW Marine Geologist and a lifelong association between us. His estuary results for commercial sand mining purposes were negative, but through drilling, dating, sedimentology and evolutionary studies of estuaries he has become internationally recognised. Peter retained a strong interest in heavy minerals in his work on coastal barrier deposits and on offshore sands. This work culminated in his epic review in 1999 in Economic Geology (v 94, 567-588) entitled “Heavy mineral beach placers in southeastern Australia: their nature and genesis”.
In this paper, Peter showed how different fractionation mechanisms concentrate heavy minerals during marine transgression and highstand sea level conditions. Four different types of deposits have been identified; three are linked to beach processes and form “beach placers”, the fourth is the product of wind deposition in coastal dunes. He shows how fractionation mechanisms are so well suited to the geological history and environmental conditions of the east coast. This includes low rates of clastic sediment supply (but unlike southern Australia not replaced by a “carbonate factory”); long periods of weathering and abrasion of sand grains in the marine environment to create a “mature” HM suite; and an energetic wave (and wind) environment that over different periods of the late Quaternary involving sea level change drove sand masses onshore and alongshore. Peter’s other contributions in searching for minerals offshore and in the Murray-Darling Basin cannot be forgotten—another story?
In working with Peter and others such as Cheng Ly, I have gained some understanding of heavy mineral deposition. Moreover, pit exposures created by miners, and access to drilling and survey records of different sand mining companies, offered rare opportunities in the 1970s to examine coastal stratigraphy and to date buried surfaces. In one paper Peter and I used company cross sections within a highly mineralized sediment compartment at Cudgen to show the pattern of lenses of heavy minerals deposited by waves (Type C in a prograded barrier subjected to episodic influxes of HM-rich sand within a quartz dominated “host” mineral) (Journal of Sedimentary Petrology, 1985, v. 55, 257-264, Fig.4). Our work with others in Port Stephens-Myall Lakes area (ANU Monograph 1992) also highlighted examples of Type C deposits and of Type B. I was gob-smacked one day in visiting a mining pit in washover deposits behind the prograded barrier north of Hawks Nest. Here landward-dipping, parallel bedding of HM-rich grains formed part of an extensive backbarrier flat (Type B deposit). Nearer to Seal Rocks we studied pits and drilled holes in dunes containing lower percent content HM than in placer deposits. These pits offered insights into aeolian processes (Type D deposits). Sand islands such as Stradbroke in southern Queensland have been mined for their low-grade HM in extensive coastal dunes .
Sand mining on the east coast has more or less disappeared. It has left a legacy of destruction coupled with attempts to restore coastal landscapes. Controversies that communities and governments faced will be explored in the next blog. Yet sand mining has provided sources of information that has enhanced our knowledge of coastal processes and evolution along this coast.
Words by Prof Bruce Thom. Please respect the author’s thoughts and reference appropriately: (c) ACS, 2023. For correspondence about this blog post please email firstname.lastname@example.org