Summary:
The mineralisation observed at the Authier project in the spodumene-bearing pegmatites is principally lithium with trace amounts of beryllium, molybdenum, tantalum, niobium, cesium and rubidium.
Detailed logging of drill core suggests that the main pegmatite at Authier is composed of several internal phases related to intrusive placement and progressive cooling. The outside border of the pegmatite in contact with the host rocks has been identified as a transition zone or border zone. This transition zone is often significantly less mineralised in spodumene and is characterised by a centimetre-scale fine to medium-grained chill margin, followed by a medium to coarse-grained decimetre to metre-scale zone. The transition zone often includes fragments of the host rock and can also be intermixed with the material from the core zone.
The main intrusive phase observed in the pegmatite is described as a core pegmatitic zone characterised by large centimetre-scale spodumene and white feldspar minerals. The core pegmatitic zone shows internally different pegmatitic phases characterised by different spodumene crystal lengths, ranging from coarse-grained (earlier) to fine-grained (later). The contacts between different spodumene-bearing pegmatite phases are transitional and well defined at core logging scale. Higher lithium grades are correlated with higher concentrations of larger spodumene crystals. Late mineral to post-mineral aplite phases cut earlier spodumene-bearing mineralisation, causing local diminishing of lithium grade. The core zone hosts the majority of the spodumene mineralisation at Authier.
The spodumene-bearing pegmatite is principally defined by one single continuous intrusion, or dyke, that contains local rafts or xenoliths of the amphibolitic host rock, which are a few metres thick and up to 200 m in length at shallow levels within the western zone. The main pegmatite outcrops in a small, 50 m by 20 m, area at the central-eastern sector that orients east-west and is mostly covered by up to 10 m of overburden. Based on the information gathered from the drilling, the pegmatite intrusion is more than 1,100 m in length and can be up to 60 m thick. The intrusion is generally oriented east-west, dips to the north at angles ranging between 35° and 50° and reaches depths of up to 270 m below surface in drilling, to date.
A second spodumene-bearing pegmatite, not visible from the surface, was intersected by diamond hole AL-16-10 at shallow levels, between 15 m and 22 m downhole depth, approximately 400 m north of the main pegmatite. Follow-up drilling in early 2017 and 2018 outlined this new body, the Authier North pegmatite, which has a strike extension of 500 m east-west, 7 m average width, gently dipping 15 degrees to the north. The Authier North pegmatite appears at shallow levels, 15 m to 25 m vertical depth, and is open in all directions.