The potentially economic lithium mineralisation in the Arcadia pegmatites is dominated by petalite and spodumene. Petalite appears to have crystallised prior or co-genetically with primary spodumene. Secondary mineralisation resulted from the alteration of primary petalite and spodumene to SQI (Spodumene, quartz intergrowth) and eucryptite respectively.
The paragenetic sequence of lithium and other major minerals at Arcadia is shown below. For the Arcadia pegmatites, quartz, microcline, petalite and spodumene occurred during the formative stages of the pegmatites as part of the initial magmatic event, represented by the solid black line. Eucryptite formed after petalite and spodumene crystallised, as an alteration product, represented by the dashed line. Lepidolite and hectorite occur during the latter stages of pegmatite petrogenesis and are relatively minor in abundance.
Prospect has embarked on a detailed mineralogical study utilising XRD on >800 samples drawn from both the Main Pegmatite as well as the Lower Pegmatite, and from within the conceptual pit design.
Results to date show that the Lower Pegmatite contains five times more spodumene (15%) than petalite (3%), and has similar gangue mineralogy to the Main Pegmatite. The XRD results completed to date on the Lower Pegmatite show a broad mineralogical zonation through the Lower Pegmatite based on the spodumene - petalite ratio and quartz content. Sampled holes located within the modeled Lower Pegmatite display higher spodumene - petalite ratios along the edges and towards the upper contacts and a higher spodumene - petalite ratio in the central and lower portions of the Lower Pegmatite. The quartz content tends to be higher in the high spodumene zones; this can be ascribed to the re-equilibration post crystallization of the petalite to form spodumene-quartz intergrowths (SQI) in the slower cooling central, and to a lesser extent in the lower portions, of the pegmatite.
Initial results from the Main Pegmatite suggest approximately equal quantities of spodumene and petalite (around 11 – 13%), with 39% quartz, 33% feldspar, and the balance largely muscovite.