Abstract:
A reconnaisance airborne magnetic survey was undertaken over the Awhitu Peninsula, covering an area of approximately 3200 km2, (A total of 650 line kilometres were flown.). The aim was to delineate concentration patterns of exposed and concealed titanomagnetite sands, and to assess the total titanomagnetite ore reserves in this area.
The data outlined four areas with titanomagnetite deposits, in addition to the well known, and presently mined deposit at Waikato North Head.
The larger deposits on land form an elongated belt of Holocene dunesands, lying immediately to the north of the Waikato North Head Deposit. Significant but smaller deposits of enriched sands occur in the Northern Area, near the tip of the Awhitu Peninsula. Here they are embedded in older Pleistocene sediments, which probably predate all ironsands on the peninsula. The Central Area contains both Holocene and older deposits. Larger deposits occur in an elongated belt 2.5 to 5 km offshore from the peninsula, and appear to be discontinuous and irregular.
The results of detailed 2-D and 3-D models of selected deposits were used to assess the reserves of the area studied.
In addition to the deposits at Waikato Heads, a total of 150 x 10 6 tonnes of concentrate was inferred to lie above sea level on the Awhitu Peninsula. Of this, approximately 100 x 10 6 tonnes are contained within the Holocene dunesands of the Mitiwai Formation. The remainder are contained within older deposits in the Northern Area. A minimum of 270 x 10 6 tonnes of concentrate were estimated for the offshore deposits adjacent to the peninsula.
In addition, two previously unknown centres of basaltic volcanism have been detected on the eastern side of the peninsula, marking the western most occurence of Pleistocene basalts of the Manakau Lowlands.