Chase Mining Corporation Ltd (ASX:CML) has expanded its Barkly North Rare Earths Project in the Northern Territory, picking up two adjoining exploration licences to the northwest.
This secures a 160-kilometre linear extent of the rare earths trend revealed by a Geoscience Australia (GA)-conducted North Australian Geochemical Survey.
The company’s management and consultants believe that this “extraordinary” trend in stream sediment rare earth element (REE) anomalism is caused by previously unrecognised ionic clay hosted rare earths mineralisation.
Rare earths potential
GA’s North Australian Geochemical Survey covered the entire Barkly region west of Mount Isa with widely spaced stream sediment samples of various sieve sizes and with a variety of analyses for all elements.
A CML study of this very large public database revealed this continuous 160-kilometre trend of peak rare earth anomalism with accompanying high values in supporting elements, notably niobium chrome and uranium.
The project area is covered by lateritised sediments with strongly developed clayey soil profiles and the trend bears no relationship to the underlying basement rocks or to magnetic features.
Ionic clay rare earths deposits have advantages over hard rock rare earth deposits. They are cheaper to mine and process, and waste material does not present problems with toxic elements. Much of the world’s supply comes from clay-hosted deposits.
Base metal potential
Along with prospects for ionic rare earths, the Barkly North project area has had a long-recognised potential for major base metals deposits in the underlying unexposed older sequences.
These sequences include those that host the major shale-hosted and IOCG deposits in the McArthur River and Mount Isa districts.
A core hole drilled in the centre of the project by BHP Ltd in 1993, MD1, intersected a 100-metre-thick black dolomitic shale with scattered copper lead and zinc sulphides. At the time, a lack of data to guide exploration hampered efforts to select drill sites as follow up holes.
Surveying solved problem of lack of data
GA has tackled this problem by conducting its comprehensive seismic and gravity surveys and publishing the results. This recent, detailed gravity data is proving very useful and has revealed a nonmagnetic gravity trend arcing through MD1.
This has provided CML with a target for future follow up geophysics and possible drilling.
Non-magnetic gravity ridges such as this are most likely to represent the dense prospective pyritic dolomitic shale which hosts the mineralisation intersected in the BHP drill hole.
Exploration rush triggered
Further west, within the new exploration licence application areas, the GA-detailed gravity survey outlined other gravity targets, some of which are magnetic. The adjacent or combined magnetic and gravity responses are typical of iron oxide copper gold (IOCG) styles of mineralisation.
The depths of these western targets are unknown but they can be calculated by modelling the new detailed data.
GA has verified the existence of IOCG-style alteration and mineralisation in the Barkly region. It has drilled combined gravity and magnetic targets through similar cover, about 250 kilometres to the south of the project, and has triggered an exploration rush in that area.
Offer of exploration licence
Previous CML EL application 33130 has been offered for grant and it is estimated that EL 33128 and 33129 will also be offered over the next few months. The newer applications for EL 33229 and EL 33230 are expected to be granted before January 2023.
CML proposes to conduct more surface sampling throughout the project area once the licences are granted in order to better define and identify the sources of the rare earths.
It is anticipated that a program of shallow drilling traverses will then allow the confirmation of a mineral resource.
The gravity and magnetic targets will be modelled, and those that are confirmed as being caused by rocks at reasonable depths may be further investigated with more geophysics and drilling.