Basin Evolution and Unconformity-Related Uranium Mineralization: The Camie River U Prospect, Paleoproterozoic Otish Basin, Quebec

Abstract

The Paleoproterozoic Otish Basin, Quebec, hosts several uranium prospects that until recently remained underexplored and poorly understood. In this study, the Camie River U prospect, which shows similar characteristics to high-grade unconformity-related U deposits, is the focus of an integrated basin analysis in the western Otish Basin. Conglomerate and sandstone of the Indicator Formation, which were deposited in at least six depositional sequences, were affected by insignificant early diagenetic compaction and cementation. This allowed the formation of regional peak diagenetic aquifers, which became muscovite altered due to interaction with fluids having δ 18 O and δ 2 H values similar to those of seawater-influenced basinal brines at 250°C. U mineralization at Camie River occurred at 1721 ±20 Ma based on a 207 Pb/ 206 Pb date obtained by laser ablation of uraninite, which coincides with a phase of the Otish Gabbro intrusion that has been dated at ca. 1730 Ma. The intrusive event promoted circulation of U-bearing basinal brines, triggering U mineralization at several locations in the western Otish Basin. Interaction of basinal brines with the Otish Gabbro produced coarse-grained chlorite, tourmaline, and phengitic muscovite, which decreased the fluid-conducting capabilities of diagenetic aquifers and resulted in fault zone-and fracture-dominated fluid flow. Subsequent fluid alteration events produced limited U remobilization, sulfides, sudoite, and siderite between ca. 1670 and 1410 Ma based on mineral paragenesis and 40 Ar/ 39 Ar dates of muscovite. Metamorphic fluids having high δ 18 O values and temperatures around 300°C accompanied 1.2 to 1.0 Ga Grenville orogenesis and subgreenschist-grade metamorphism in the Otish Basin but were present at low water/rock ratios at Camie River and therefore produced little alteration. Post-Grenville uplift of the Otish Basin likely produced late, low-temperature alteration minerals that have been influenced by recent meteoric water, suggesting that the fault zones and fractures the minerals occupy remain as preferential fluid-flow pathways to the present day. Radiogenic Pb and the characteristic trace elements Mo + W + Nb have also preferentially dispersed from the mineralization along fault zones, fractures, and depositional sequence boundaries, and can be used to explore for Camie River-style U mineralization.

Formation of the enigmatic Matoush uranium deposit in the Paleoprotozoic Otish Basin, Quebec, Canada

“…1.75 Ga, when the youngest dykes and sills identified as the Otish Gabbro intruded the Otish Group (Fahrig and Chown 1973;Chown and Archambaul 1987;Beyer et al 2012 and discussion within; Fig. 1).…”

“…Two major lithofacies are observed in the Indicator Formation (Beyer et al 2012). Lithofacies 1 consists of relatively thickly bedded, massive to trough cross-bedded cobble to granule conglomerates.…”

“…2) described in historical Matoush drill hole logs from the exploration company Uranerz Energy Corporation. Lithofacies 2 contains thinly bedded, rippled to laminated, medium-to coarse-grained quartz arenite to subarkosic arenite that were deposited in lower-energy braided stream channels or unconfined sheetfloods in a braid delta setting, based on the smaller grain size, sedimentary structures, and intermittent mudstone content (Beyer et al 2012). Lithofacies 2 is equivalent to the Channel Bar Facies (CBF; Fig.…”

“…1). The Beaver Lake mineralization is hosted in basement rocks consisting of biotite-cordierite gneiss and biotite schist (Gatzweiler 1987), whereas the Camie River deposit is situated at the unconformable contact between an Archean basement and the overlying Indicator Formation (Gatzweiler 1987;Beyer et al 2012). The Camie River U mineralization consists mostly of uraninite and extends 20 m into the basement and 50 m along fractures into the Indicator Formation (Gatzweiler 1987).…”

“…1). This basin hosts several uranium showings, including a significant unconformity-related prospect, Camie River, situated on the south margin of the basin (Gatzweiler 1987;Beyer et al 2012).…”