The Molyhil tungsten-molybdenum project is an open-pit mining project proposed to be developed by Thor Mining priority in the Northern Territory of Australia.
The Molyhil licence was originally held by Petrocarb Exploration which produced approximately 900,000 tonnes (t) of ore from the deposit until 1982. The mine ownership was subsequently changed several times before it was finally being acquired by Thor Mining in early 2005.
Although Thor Mining completed a definitive feasibility study (DFS) to expand the existing open-pit at Molyhil in 2007, the project couldn’t proceed due to the global economic crisis in 2008.
An updated DFS for the project, completed in July 2018, predicted a total production of 8,583t of tungsten oxide and 3,133t of molybdenum over an initial mine life of seven years with an estimated capital expenditure of approximately £40m (A$69m).
The Northern Territory Government recognised it as a major project and signed a project facilitation agreement (PFA) with Thor Mining in July 2020.
A final investment decision (FID) on the project is expected by the end of 2021, while the construction works are is expected to be started in 2022 with the start of production anticipated in 2023.
Location, geology, and mineralisation
Molyhil tungsten-molybdenum project is located near the town of Hart in the Northern Territory, approximately 220km north-east of Alice Springs. Marshall River and Dulcie Range National Park lie in close proximity to the mine.
The project site is located within the prospective polymetallic province of the Proterozoic Eastern Arunta Block, at an elevation of approximately 400m above the sea level.
The Molyhil tungsten-molybdenum deposit forms part of the Neoproterozoic Georgina Basin and the Paleoproterozoic Strangways Metamorphic Complex. It comprises two north-south trending iron-rich skarn bodies containing scheelite and molybdenite mineralisation. The scheelite and molybdenite occur in calc-silicate rocks, while the other minerals associated with the ore are chalcopyrite, pyrite, and magnetite.
The molybdenum and tungsten mineralisation Molyhil are found coarse-grained in hornfels unit rich in magnetite and sulphide.
Tungsten and molybdenum reserves at Molyhil
The Molyhil mine is estimated to hold 3.5 million tonnes (Mt) of probable ore reserves grading 0.29% tungsten and 0.12% molybdenum.
The total indicated and inferred resources are estimated to 4.7Mt grading 0.28% of tungsten, 0.14% of molybdenum, 0.05% copper, and 18.8% iron.
Mining and ore processing
The Molyhil tungsten-molybdenum project involves the expansion of the existing open-pit that measures 150m-long, 120m-wide, and 13m-deep.
The conventional open-cut mining method involving contract drill and blast followed by owner-operated excavation and haulage operations will be employed for the project.
The run-of-the –mine ore will be sent to a nearby processing plant where it will undergo two-stage crushing, X-Ray (XRT) ore sorting, and two-stage of grinding in a rod and a ball mill before passing through a four-stage flotation circuit for the production of tungsten and molybdenum concentrate.
Infrastructure facilities for the Molyhil project
The project site is accessed via the Plenty Highway, which is a partially sealed road off the Stuart Highway that connects Alice Springs and Darwin.
The project is planned to be operated as a fly-in and fly-out operation with provision for camp and electricity generation. Water will be procured from the underground aquifers located nearby.
RPM Global provided the resource estimates while AVCS provided the open-cut ore reserve statement for the updated DFS of the project.
Rosetta Stone Ops provided the capital costs estimates, while KYSPY Investments was consulted for the metallurgical processes and outcomes.
Keith Lindbeck & Associates was engaged in environmental studies and Mazars Global Infrastructure Finance provided the project’s economic model.