Highland Plains, Northern Territory, Australia

Project overview

The Highland Plains Phosphate Project in the Northern Territory comprises of one granted exploration lease (36.9 km2) and two exploration lease applications (818.9 km2) which are 100% owned by Gibb River Diamonds Limited (ASX: ‘GIB’ or the ‘Company’). The project is located close to Australia’s northern coast and to Asian markets.

  • The project has a total JORC (2004) compliant Inferred Resource of 56 million tonnes at 16% P2O5 at a 10% P2O5 cut-off.
  • Contained within this Global Resource (above) is an Inferred Resource of 14 million tonnes at 20% P2O5 (above a 15% P2O5 cut-off), confined to the western portion of the Global Resource. This is named the Western Mine Target Zone (WMTZ).
  • Positive metallurgical test work so far has established a method of beneficiation with excellent recoveries. The best flotation test to date gives a grade of 32.3% P2O5 (upgraded from 23.4% P2O5) at 76% recovery of phosphate.
  • Highland Plains Phosphate has low levels of the contaminants C (0.2%), S (0.06%), F (1.82%), Cl (112ppm), Cd (4ppm) and U (38ppm).
  • GIB is seeking a strategic investment partner to progress the project through feasibility studies and into production.

Figure 1: Highland Plains Phosphate Project and Logistics Distances

Geology and Mineralisation

The Highland Plains phosphate deposit is hosted by the Border Waterhole Formation in the Georgina Basin. Prior geological studies delineated two major tabular phosphatic intervals in the lower part of the formation. The lower of these (1.5–17m thick) is at the formation base. Some 7–17 m stratigraphically above this, the upper interval, which is 1.5–11 m thick.

To date, GIB has spent more than $10 million on exploration in the area, and together with historical drilling in the 1960s, the area has been subject to more than 80 air core/reverse circulation drill holes for more than 2,100m and 7 diamond drill holes for 136m.

The project has a total JORC (2004) Inferred Resource of 56 million tonnes at 16% P2O5 at a 10% P2O5 cut-off. The Western Mine Target Zone (WMTZ), a subset of the total resource, is shallower and has higher grade JORC Inferred Resource of 14 million tonnes at 20% P2O5 with a 15% P2O5 cut-off. Areas of the WMTZ outcrop and have been bulk sampled by the Company using a backhoe.

The Company has also identified a number of future exploration targets on EL25068, with potential to expand the known resource.

Figure 2: Highland Plains Phosphate Project Plan View


Figure 3: Highland Plains Phosphate Project Section View


Highland Plains – Minor Elements

All phosphate deposits have varying levels of impurities. Previously reported work at Highland Plains has indicated impurity levels for a 22.9% P2O5 (un-beneficiated) rock as being:

C (0.2%); S (0.06%); F (1.82%); Cl (112ppm); Cd (4ppm) and U (38ppm);

The levels of these contaminants could be considered low.

Pb: A limited number (74) of phosphate bearing sample pulps were previously assayed for further trace elements including Pb (POZ/GIB Quarterly Report to ASX dated 1 October 2012). Elevated lead values occurred in isolated areas proximal to the base of the lower phosphate beds where they directly overlie basement Proterozoic rocks; this effect is possibly related to post-mineralisation groundwater movement concentrating lead at the geological unconformity. These areas of elevated lead could potentially be mitigated through selective mining practices or beneficiation7.

Further drill and assay work is required to model these impurities within the overall resource.

Impurity levels for specific elements for 34.8% P2O5 (beneficiated product) were reported in the GIB/POZ ASX Release dated 19 March 20103.

Further work

The Company is seeking a strategic investment partner to progress the project through feasibility studies and into production. Further work would include:

  • Further drilling and assay work to upgrade the deposit to a JORC (2012) Indicated and Inferred Resource
  • Metallurgical Bench Scale testwork to assess beneficiation effects on lower head grade material and to determine the engineering properties of the material
  • Metallurgical pilot plant testing of bulk samples for phosphate grade and purity enhancement
  • Geological modelling of areas containing to balance grade and other elements
  • Further logistical studies and modelling
  • Mine planning and optimisation
  • Budgeting, planning and timelines to production
  • Publishing a Scoping Study leading into a full Bankable Feasibility Study (if required)


Highland Plains is located on the Northern Territory’s border with Queensland, and offers multiple potential transport and logistics options for exporting phosphate. This includes a slurry pipeline to transport the phosphate to one of a number of coastal locations, where it would be dewatered and loaded onto a coastal barging operation with transhipment to bulk carriers, in a process similar to existing operations at Port Karumba or Port Bing Bong. The potential slurry pipeline distances range from 220 km to 374 km.

Highland Plains is also only 68 km from existing infrastructure at the Century Zinc Mine where New Century Resources is producing zinc concentrate from a tailings retreatment operation. This mine already has in place mains power, a beneficiation plant and an existing slurry pipeline to transport product to Port Karumba for export via a barge with transhipment to a larger vessel in the Gulf of Carpentaria.


Tenements EL 33304 and EL33305 (Figure 2) are considered highly prospective for new phosphate discoveries. These leases are proximal to the Company’s existing Highland Plains Phosphate Project and target the same embayment style of phosphate mineralisation to that found at Highland Plains. This extends the Phosphate Project area held by GIB by a further 818.9km2.

Figure 4: Highland Plains Phosphate Project Exploration Tenements Plan View

Highland Plains Phosphate Metallurgical Flotation Testing

Highland Plains Bulk Sampling High Grade Phosphate at Surface


1Maiden JORC Resource at Highland Plains; POZ/GIB ASX Release dated 31 March 2009
2Quarterly Report; POZ/GIB ASX Release dated 29 October 2009
3Metallurgical Update (#4); POZ/GIB ASX Release dated 19 Mar 2010
4Quarterly Report; POZ/GIB ASX Release dated 29 July 2010
5Quarterly Report; POZ/GIB ASX Release dated 29 Oct 2010
6Further Positive Results from Metallurgical Testing (#2); POZ/GIB ASX Release dated 21 Dec 2010
7Quarterly Report; POZ/GIB ASX Release dated 1 October 2012

The Information in this report that relates to the previously reported Highland Plains Mineral Resource and previously reported Highland Plains exploration and metallurgical data is based on information compiled by Jim Richards who is a member of the Australasian Institute of Mining and Metallurgy and a Member of the Australian Institute of Geoscientists. Jim Richards is a director of Gibb River Diamonds Limited and has sufficient experience which is relevant to the style of mineralisation and type of deposit under consideration and to the activity which they are undertaking to qualify as a competent Person as defined in the December 2004 Edition of the Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves. Mr Richards consents to the inclusion in this report of the Information, in the form and context in which it appears.

The Highland Plains Mineral Resource Estimates (MRE)’s were prepared and first disclosed under the JORC Code 2004. It has not been updated since to comply with the JORC Code 2012 on the basis that the information has not materially changed since it was last reported. The Company confirms that the form and context in which the Competent Person’s findings are presented here have not been materially modified.