The Hope Downs mine is located in the Hamersley Group which forms the middle layer of Mount Bruce Group in the Marra Mamba Iron Formation.

The Marra Mamba Iron Formation is the lowermost unit of the Proterozoic Hamersley Group in the northwestern part of Western Australia.

The Marra Mamba Iron Formation varies considerably in thickness, as based on sections measured in the field; however, not enough drill hole data are available to provide a quantitative assessment of its thickness variation throughout the Hamersley Range. Trendall and Blockley repoft a thickness range of 183 to 229 m based on sections mearPresent address: Department of Geology, Georgia State Univcrsity, Atlanta, Georgia

Others report thicknesses that range from a minimum of 15 m to 183 m (Macleod, 1966) for sections in different parts of the Hamersley Range. The Marra Mamba lron Formation is underlain by the Jeerinah Formation which is the uppermost member of the Fortescue Group. This group may be as much as 3660 to 4270 m thick and consists of shales and cherts in the upper part.

Rio Tinto operates Hope Downs 1 and Hope Downs 4 mines via Joint venture between Rio Tinto and Hancock Prospecting.

Mining Operations
Hope Downs mines are conventional open pits using track and shovel mining method with preliminary drilling and blasting. The drill holes are filled with an explosive, most often ANFO (Ammonium Nitrate/Fuel Oil) and then charged. The resulting blast breaks the material to a size required for digging.

The broken material is loaded for transport by face shovels, excavators or front-end loaders into haul trucks. Haul trucks at our operations are typically in the 190 tonne and 240 tonne class. Overland conveyors are used to transport partially crushed feed at sites where there are long distances between the pits and process plants.

Hope Downs 1 mineralisation occurs as goethite/ haematite within the banded iron formations of the Marra Mamba Fm. Some detrital mineralisation also occurs. Hope Downs 1 is processed at the Hope Downs 1 process plant which is dry crush and screen plant producing a lump and fines product. Ore from Hope Downs 4 is processed through the Hope Downs 4 processing plant. Wet scrubbing and screening are used to separate lump and fines products, prior to desliming of fines product using hydrocyclones.