Amy Cleaver HBSc thesis abstract

Thesis Title: 
Mineralogy and Petrology of the Good Hope Carbonatite Occurrence, Marathon, ON

The Good Hope Carbonatite Occurrence is a recently discovered high grade niobium and phosphate occurrence located adjacent to the Prairie Lake Carbonatite Complex, approximately 45 kilometres northwest of Marathon and about 28km North of Highway 17 (49˚ 02’ N, 86˚ 43’ W).  This study focuses on the paragenesis and classification of the pyrochlore-group minerals of the Good Hope occurrence. Minerals identified include calcite (CaCO3); ferrodolomite (CaFe(CO3)2); siderite (FeCO3); apatite (Ca5(PO4)3(OH,F,Cl);  ferrocolumbite (FeNb2O6); fersmite (Ca,Ce,Na)(Nb,Ta,Ti)2(O,OH,F); and pyrochlore(A16-xB16O48(O,OH,F)8-y·zH20). Less common minerals include: ankerite (Ca(Mg,Fe)(CO3)2); synchysite (CaCe(CO3)2F); bastnaesite (Ce(CO3)F); parisite (CaCe2(CO3)3F2); quartz; rutile; pyrite; magnetite; and barite. Two paragenetic varieties of carbonatite were recognized on the basis of mineral abundances and the textures. These are referred to as the pyrochlore-rich and pyrochlore-poor phases.  The difference between the two phases is interpreted to suggest that the pyrochlore-poor phase represents a later stage of crystallization. The pyrochlore in the pyrochlore-rich phase are intimately intergrown with coarse-grained apatite and are interpreted as clasts derived from early-forming cumulate. The niobium mineralization is dominated by pyrochlore, which exhibits complex replacement textures involving both fersmite and ferrocolumbite. On the basis of textural evidence a definitive crystallization order or relationship between pyrochlore, fersmite and ferrocolumbite could not be established. The pyrochlore is dominated by Na-Ca pyrochlore with minor amounts of Sr-pyrochlore present only in drill core samples. The compositions of pyrochlore show a transition from magmatic to an alteration trend with drill core samples being more altered than surface samples. The latter are considered to be dominantly of a magmatic origin, whereas the drill core pyrochlore are considered to have been affected by hydrothermal processes. Our data indicate easy ore beneficiation due to the presence of only one significant niobium-bearing phase with limited compositional variations. The pyrochlore also does not contain significant amounts of U or Th, which increases its economic potential as these elements can cause environmental concerns involving radioactive refinery residues.

The mineralogy of the Good Hope carbonatite occurrence is different to that of carbonatites occurring in the western and southern margins of the Prairie Lake Carbonatite Complex. The latter are dominated by olivine, calcite, fluoroapatite, Ti-magnetite and phlogopite-tetraferriphlogpite, with niobium mineralization dominated by include Na-Ca pyrochlore, latrappite, loparite, U-pyrochlore, Ce-pyrochlore and Pb-pyrochlore. These differences, coupled with different magnetic signature, carbonatite texture, weathering profile and distinct topography, indicate that the Good Hope carbonatite occurrence is perhaps not directly related to the Prairie Lake carbonatite rock; however, the actual genetic relationship remains unknown.