Fenn Gap Iron/Manganese Prospects, Standley Chasm, MacDonnell Region, Northern Territory, Australiai

Regional Level Types
Fenn Gap Iron/Manganese Prospects	Group of Prospects
Standley Chasm	- not defined -
MacDonnell Region	Region
Northern Territory	Territory
Australia	Country

The Fenn Gap iron/manganese prospects, are several outcropping deposits, trending east-west, between the Larapinta Drive to the north, and Heavitree Ridge to the south. The deposits strike a length of almost 10 kilometres between the Simpsons Gap, and Standley Chasm turn-offs. Fenn Gap itself, is about half-way along the line of prospects, to the south, cutting through the quartzite Heavitree Ridge. The prospects are 25-35 kilometres west of Alice Springs.

Several named prospects outcrop over a length of 10 kilometres as stratabound dolomite hosted manganese rich zones, with manganese grades up to 50.9% Mn (averaging 39% Mn), with goethite to 41.6-57.7% Fe. Discovered by NTGS mapping in 1970. Drilling from 2010 revealed limestone and dolomite hosting goethite, hematite and limonite associated with chert lenses.

The mineralisation is hosted by the Bitter Springs Formation, which dips steeply south. The prospects are 30-40 metres wide, and over 100 metres deep as alteration zones of goethite with secondary manganese. The alteration zones are complex, occupying individual dolomite beds, containing chert breccia lenses, along trends of cross faults.

A.L. Maynard and Associates suggest the breccia represent salt welds from the extrusion of the Gillen Salt Member on the northern edge of the Amadeus Basin, with the breccia left behind as a residual deposit, with goethite as the primary mineral, then manganese leached from surrounding rocks, and scavenged by the goethite. It represents a late stage supergene enrichment, with manganese fluids invading fissures and vughs in the goethitic breccia.
Generally the prospects show goethite alteration on the south side of the chert breccia, and manganese enrichment in carbonate units on the north side.

There are several named pods and lense prospects, from west to east are the West, Fenn Gap, Knob Hill, Black Ridge, Hole Hill, Table, and Round Hill prospects.

Large scale open pit strip mining here is highly unlikely for a number of reasons. First is the moderate levels of iron and manganese. Within the immediate area are several homes of the local aboriginal landholders. Nearby are national parks and the prospects are within an area considered of natural beauty and heavily used by tourists.

The U.S/Australian Pine Gap spy base is a short distance to the south.

Other Regions, Features and Areas containing this locality

References