The sandstone-hosted Beverley uranium deposit is located in terrestrial
sediments in the Lake Frome basin in the North Flinders Ranges, South
Australia. The deposit is 13 km from the U-rich Mesoproterozoic basement
of the Mount Painter inlier, which is being uplifted 100 to 200 m above
the basin by neotectonic activity that probably initiated in the early
Pliocene.
The mineralization was deposited mainly in organic matter-poor Miocene
lacustrine sands and partly in the underlying reductive strata
comprising organic matter-rich clays and silts. The bulk of the
mineralization consists of coffinite and/or uraninite nodules, growing
around Co-rich pyrite with an S isotope composition (delta S-34 = 1.0
+/- 0.3 parts per thousand), suggestive of an early diagenetic
lacustrine origin. In contrast, authigenic sulfides in the bulk of the
sediments have a negative S isotope signature (delta S-34 ranges from
-26.2 to -35.5 parts per thousand), indicative of an origin via
bacterially mediated sulfate reduction. Minor amounts of Zn-bearing
native copper and native lead also support the presence of specific,
reducing microenvironments in the ore zone. Small amounts of carnotite
are associated with the coffinite ore and also occur beneath a paleosoil
horizon overlying the uranium deposit.
Provenance studies suggest that the host Miocene sediments were derived
from the reworking of Early Cretaceous glacial or glaciolacustrine
sediments ultimately derived from Paleozoic terranes in eastern
Australia. In contrast, the overlying Pliocene strata were in part
derived from the Mesoproterozoic basement inlier. Mass-balance and
geochemical data confirm that granites of the Mount Painter domain were
the ultimate source of U and BEE at Beverley. U-Pb dating of coffinite
and carnotite suggest that the U mineralization is Pliocene (6.7-3.4
Ma).
The suitability of the Beverley deposit for efficient mining via in situ
leaching, and hence its economic value, are determined by the nature of
the hosting sand unit, which provides the permeability and low
reactivity required for high fluid flow and low chemical consumption.
These favorable sedimentologic and geometrical features result from a
complex conjunction of factors, including deposition in lacustrine shore
environment, reworking of angular sands of glacial origin, deep Pliocene
weathering, and proximity to an active fault exposing extremely U rich
rocks.