Summary:
Deposit Types
The deposit model at the Eldor Property is a carbonatite-hosted REE-Nb-Ta deposit. Carbonatites are by definition igneous rocks, intrusive and extrusive, which contain more than 50% by volume of carbonate minerals such as calcite, dolomite, ankerite, and less often siderite and magnesite. Intrusive carbonatites occur commonly within alkalic complexes or as isolated intrusions (sills, dikes, breccias, or small plugs) that may not be genetically related to other alkaline intrusions.
Mineralization
The REE mineralization at Ashram is hosted primarily (essentially 100%) by monazite, with minor rare earth fluorocarbonates (bastnäsite, parisite, and lesser synchysite) and lesser xenotime. Rare earth mineralization at Ashram is consistent throughout the Deposit with minimal dilution from unmineralized fragments and clasts.
The principal heavy rare earth mineral is xenotime-(Dy) present as anhedral to subhedral crystals in association with nioboaeschynite, niobian rutile, ferrocolumbite, monazite, quartz, and mica. Xenotime is present in either pools of quartz, small veins (mm) in fluorite ferrocarbonatites, or scattered throughout the carbonatite as a trace mineral in association with disseminated monazite and/or bastnäsite.
At least two generations of monazite are present: one associated with fluorite and/or disseminated in dolomite, and a second associated with the xenotime mineral assemblage. The xenotime mineral assemblage represents a distinct (later) mineralization event from that formed the first generation of monazite.
The Ashram Deposit can be roughly divided into four main mineralized zones termed ‘A-Zone’, ‘B-Zone’, ’Breccia (Classic)’ and ‘BD-Zone’. In general, A-Zone is central to the Deposit and is rimmed by B- Zone and BD-Zone respectively. This relationship is more prevalent along the western margin of the Deposit, where the BD-Zone is in contact with an unmineralized fenite, which interfingers with and transitions to a none-REE mineralized carbonatite unit. Along the eastern margin of the Deposit, the B and BD zones relationship is more variable, with unmineralized carbonatite predominantly marking the contact, with the fenite unit noticeably being absent. The Breccia (Classic) crosscuts ‘A-Zone’, ‘B- Zone’, and ‘BD-Zone’ at depth and can be traced as thinning dyke to near surface at the western margin.
A-Zone
The A-Zone lithology is the largest unit by volume and surface footprint, and also the most highly mineralized of the Ashram Deposit (typically 1.5-3+% TREO). The unit is typically very fine- grained, light to dark olive-grey, and composed of clasts of breunnerite (magnesian siderite) plus fluorite, or fluorite plus monazite, set in a complex matrix of several generations of ferro-dolomite. Fluorite is typically abundant and pervasive in the zone, occurring as disseminations, blebs, patches, veins, and fracture fillings. Accessory and trace minerals include apatite, pyrite, sphalerite, magnetite, xenotime, quartz, and niobium phases (niobium rutile, nioboaeschynite, ferrocolumbite, and niobium ilmenite).
Breccia (Classic)
The Breccia (Classic) rock type is a matrix supported breccia with polymict clasts of other carbonatites and fenites. Clasts are angular to rounded and reach up to several centimetres within an aphanitic to very-fine grained REE-enriched (~1% REO) groundmass. To date, it has only been observed to occur within the Ashram Deposit. Due to clasts of calcite and dolomite carbonatite containing pyrochlore, this unit is geochemically distinguishable compared to the other REE-dolomite carbonatite rock types. Contacts to other units are usually irregular or anastomosing.
B-Zone
The B-Zone unit typically comprises cataclastic ferro-dolomites with coarser grain size and fewer fluorite-monazite clasts than the A-Zone. Visually, the B-Zone has a cream to grey colour with a pervasive, yet patchy, yellow-beige hue of mineralization comprising monazite, apatite, and carbonates. Patches of quartz-phlogopite are present with veins of niobian rutile, ferrocolumbite, and xenotime in association with quartz, phlogopite, and bafertisite also observed. Fluorite is present occasionally as locally abundant patches or blebs and may lend a bluish hue to the rock where present; sulphides are rare.
BD-Zone
The BD-Zone unit is typically cream to white in colour with orange-pink to red pervasive shades from rare earth fluorocarbonate mineralization (intergrowths of parisite-bastnäsite with lesser synchysite), and is coarser grained than the A-Zone. The BD-Zone is visually and mineralogically distinct from the A and B zones. The unit typically comprises vuggy crystalline dolomite with common to abundant rare earth fluorocarbonates (parisite intergrowths with bastnäsite) and trace to minor phlogopite, quartz, calcite, and microcline; fluorite and monazite are absent to rare. The BD-Zone may be highly blocky/fractured locally, and this is more evident along the western margins of the Deposit.
Contact Lithologies
The main unmineralized contact lithologies of the Ashram Deposit may be generally grouped as fenites, lamprophyres, and other carbonatites. Furthermore, the Eldor carbonatite is in contact with metasediments and metavolcanics.
The ‘Fenite’ rock types are wall/country rocks that have been metasomatized by a K- and Na-rich fluids derived from the intruding carbonatite. They can be identified by naked eye examination despite their heterogenic appearance. They are typically fine-grained, but may be mediumgrained in some rare cases, with dark grey/brown, blue, or green colour based on the specific mineralogy (phlogopite, Na-amphibole, or pyroxene, respectively). Fenites are almost always crosscut by multiple carbonatite veinlets that have an intensive alteration halo of phlogopite around them.