Foreshore Mining Locations
Port Waikato North Head.
At Port Waikato, BHP mines 6 M tpa of ironsand from the North Head, which is concentrated on site to produce 1.2 M tpa of titanomagnetite concentrate. Mining of the deposit began in 1969, and production to the end of 2000 is about 18 Mt of concentrate. The concentrate is slurried 18 km to the steel mill at Glenbrook where it is blended with Huntly sub-bituminous coal in the ratio of about 1.8:1 and heated in reduction kilns to form sponge iron containing 70% Fe. The sponge iron is melted in an electric arc furnace to produce molten pig iron. The resultant steel products are for domestic consumption and for export, and include very high-purity stainless steels. A vanadium-rich slag is separated as a valuable by-product. Currently 12,000 t/yr is produced and exported to China, representing 1% of the world’s vanadium production. Estimated in-ground ore resources at Waikato North Head are in the region of 140 Mt of concentrate.
At Taharoa, ironsand is mined by dredging beach and dune sand to produce concentrate averaging 40% titanomagnetite. Annual production has been about 1.4 Mt since the operation opened in 1972. The concentrate is slurried through a 3 km long pipeline to an offshore loading facility for export. Total exports to the end of 1996 were 31 Mt, mainly to Japan, with small quantities to South Korea and China. Estimated in-ground ore resources at Taharoa are about 208 Mt of concentrate.
A small land-based mining operation in the dunes behind the beach here was begun in 1971 and wound up in 1987. Like at Taharoa, ore was slurried via a pipe to ships moored offshore and transported to Japan and China. Extraction of 15 million tonnes of ore created a vast hole, which is now filled with water. A new beach-side subdivision now covers part of the site. There is currently a permit for prospecting and exploration here.
There has been a long history of mining gravel and aggregate directly from the beaches of Hawke’s Bay, beginning during the earliest period of settlement. Not having been monitored, there is only anecdotal information concerning these early beach-mining activities. For example, large volumes were extracted during the construction of the railway, needed to raise its bed.
This extraction was not limited to local needs of sand and gravel; for example, in the construction of the huge concrete pier in Tolaga Bay north of Gisborne, the gravel in its concrete came from the Hawke’s Bay beaches. In recent years the most significant extraction of beach sediment has taken place at Awatoto, which has averaged 47,800 cubic metres per year; during the 30 years from 1973 to 2002, for which we have the best records, this extraction removed a total volume of nearly 1,500,000 cubic metres of beach sediment, and continues today although this annual removal is scheduled to decrease during the next ten years, and to cease altogether after that.
The significance of this commercial extraction at Awatoto is that it has exceeded the quantities of gravel reaching this stretch of shore, from the Tukituki River and from sea-cliff erosion along Cape Kidnappers. As a result, the total quantity of gravel and sand contained within the beach between the Cape in the south and Bluff Hill and the Port’s breakwater in Napier has significantly decreased over the years, making this stretch of shore more susceptible to property erosion and flooding.
Whiritoa has been substantially transformed form its original state, when it featured huge heaped dunes. Early Māori communities removed most of the original coastal forest and dune plants. European farmers then introduced stock to the dune area, disturbing the native sand-binding grasses and causing severe wind erosion. Most of the sand reserves eroded, reducing the height of the dunes and caused sheets of sand to move more than 200m inland, then was mined for over 50 years; in total more than 180,000m³ of sand has been removed. Since the 1960s coastal subdivision has covered most of what remains of the sand dune reserves.