Prairie Downs (WA)
Overview
Dynasty's flagship Prairie Downs Iron Project is located in Western Australia’s prolific iron-producing Pilbara region.
JORC-Compliant iron resources totaling 1.4 billion tonnes have been estimated for the Spearhole Detrital Iron Deposit, which include 932 million tonnes at 27.4% Fe at a cut-off grade of 20% Fe.
Dynasty is evaluating three types of iron mineralisation at Prairie Downs:
- Detrital Channel Iron deposits which are present in very large tonnages near surface and can be upgraded to marketable grades through simple physical processing;
- Marra Mamba Iron deposits with Direct Shipping Ore (“DSO”) grades of iron; and
- Iron-rich basal conglomerate deposits.
Only about 2% of Dynasty's extensive (~4000km2), 100%-owned tenements at Prairie Downs have been drilled to date. Exploration is focussed on a number of targets within the tenements with the main area drilled to date being at the Spearhole Prospect.
Dynasty’s flagship Prairie Downs Iron Project is located southwest of the township of Mt Newman.
In parallel with drilling to assess the iron potential of this large holding, Dynasty is implementing studies that will provide a better understanding of the options to develop these substantial iron resources and form the basis of a pre-feasibility study.
Resources
Dynasty drilled more than 20,000m at Prairie Downs during 2009 and 2010.
On 27 October 2010, Dynasty announced the following JORC-Compliant Resource for the Company’s Spearhole Detrital Iron deposit (“ironstone gravel”) at Prairie Downs.
Inferred Resources - Spearhole Detrital Iron Deposit
|
Tonnes Mt* |
Fe % |
Calcined Fe* “CaFe" % |
SiO2 % |
Al2O3 % |
P % |
LOI % |
Cut-Off Grade % Fe |
| 449 | 31.5 | 34.0 | 30.2 | 13.6 | 0.04 | 7.5 | >27% Fe |
| 586 | 30.2 | 32.7 | 31.6 | 13.9 | 0.04 | 7.6 | >25% Fe |
| 800 | 28.4 | 30.8 | 33.5 | 14.4 | 0.04 | 7.7 | >22% Fe |
| 932 | 27.4 | 29.7 | 34.6 | 14.7 | 0.04 | 7.8 | >20% Fe |
| 1,118 | 25.9 | 28.1 | 36.1 | 15.0 | 0.04 | 7.9 | >17% Fe |
| 1,400 | 23.5 | 25.5 | 38.6 | 15.5 | 0.03 | 8.1 | Total Resource |
* Calcined Fe ("CaFe") = Fe/((100-LOI)/100)
On 18 March 2010, Dynasty announced the following JORC-Compliant Resource for the Company’s Marra Mamba Hematite Iron Deposit at Prairie Downs.
Inferred Resources - Marra Mamba Deposit
|
Tonnes Mt * |
Fe % |
Calcined Fe “CaFe" % |
SIO2 % |
AL2O3 % |
P % |
LOI % |
Cut Off Grade % Fe |
| 7.2 | 53.7 | 58.7 | 9.4 | 4.3 | 0.05 | 8.5 | >50% Fe |
| 23.3 | 44.2 | 48.3 | 21.9 | 5.2 | 0.04 | 8.0 | Total Resource |
* Marra Mamba Deposit density assumed at 2.8 dry tonnes per cubic metre
Geology
The complex Hamersley Formation which contains Brockman and Marra Mamba Iron Formations dominates the northern portion of Dynasty’s tenements at Prairie Downs.
Erosion of these major iron formations over the past 2.5 billion years has provided the material for vast deposits of Detrital Iron.
The Spearhole Detrital Iron Deposit occurs at or near surface, with consistent grades and thicknesses that are tending to improve as extensions of the deposit are discovered to the southeast. The detrital iron mineralisation is contained within a large, ancient, iron-enriched drainage system between outcropping Brockman and Marra Mamba Iron Formations.
The Prairie Downs Fault cuts Dynasty’s tenement package in a northwesterly direction and separates the Hamersley Formation from Bangemall Basin sediments to the south. These sediments have a coarse basal conglomerate consisting mainly of clasts of Hamersley Iron Formation rocks, or their equivalent. Gold and copper mineralisation is also present in the region.
Exploration
Exploration during 2011 is likely to include:
- Drilling to collect additional Spearhole Detrital Iron Deposit bulk samples;
- Reconnaissance exploration on Prairie Downs tenements to identify high grade hematite targets;
- Preliminary exploration on the massive iron-rich basal conglomerate; and
- Reconnaissance exploration on Dynasty’s other tenements in the Pilbara Region.
Processing Test Work
Encouraging results have been received from processing test-work on bulk samples from the Spearhole Detrital Iron Deposit.
This work indicates that a premium‐grade, high-purity DSO grade iron ore product can potentially be produced to supply niche markets as well as to provide a blend into the typical suite of Pilbara iron ores.
Test-work on a pilot sample has indicated that blended product grades can be achieved of approximately 57% Fe, 6-7% Si, 6-7% Al and 0.05% P with a yield in the order of 17%. Applying this “preliminary indicative yield” of 17% to the portion of the Inferred Resource at a cut-off grade >27% Fe (932 million tonnes at 27.4% Fe) indicates ‘at this stage’ that at least 160 million tonnes at DSO grades may be recoverable from the current resource.
This work has enhanced Dynasty’s understanding of the deposit and the high-grade zones within the gravels. It is hoped that, with more testing, increased understanding will confirm and potentially improve these results. However, it should be noted, these results require further confirmation before they can be considered a reliable indication of the grades and yields obtainable from the resource.
This test-work demonstrates that the Spearhole Detrital Iron Deposit can readily be separated from the majority of the waste material at a very low cost of <$1.00/tonne. The substantial reduction in volume for a low cost, will increase head grade to the processing plant and reduce the overall processing and transport costs, as well as enable a DSO commercial grade of iron, silica and alumina to be achieved. Phosphorous is inherently low in the Spearhole Detrital Iron Deposit.
Project Development Studies
Dynasty plans has commenced commercial investigations that will cover preliminary mine planning, beneficiation process design, mining and processing costs, transport infrastructure, capital costs, environment and native title clearances, and government approvals. These investigations will form the basis for a pre-feasibility study.
The potential development of Dynasty’s Detrital Iron deposit is likely to benefit from the following economic advantages:
- Economies of scale (>15 million tonne per annum operation);
- Low mining costs due to a low to negligible strip (waste to ore) ratio and a free digging, relatively soft, unconsolidated iron deposit;
- Simple physical processing to achieve marketable grades of iron and silica; and
- Sweet spots, high-grade zones and hematite ores all contribute to uplift average grades.
Dynasty believes that the Spearhole Detrital Iron Resource at Prairie Downs has a reasonable probability of proving to be economic to mine and beneficiate.