Application of Factor Analysis in the Identification of a Geochemical Signature of Buried Kimberlites in Near-surface Groundwaters in the Attawapiskat Area of the James Bay Lowlands of Northern Ontario, Canada

• Main Author: Drouin, Marc
• Format: Thesis
• Language: English
• Published: 2012
• Subjects: Factor Analysis; Kimberlites; Shallow groundwater; Northern Ontario; Geochemical signature; Diamond exploration; Attawapiskat; Canada; James Bay
• Online Access: http://hdl.handle.net/10393/22872

In the James Bay Lowlands of northern Ontario, kimberlite pipes are concealed by peat, thick layers of till, and Tyrell sea sediments. Studies have shown that buried ore bodies produce geochemical signatures in surface media. This thesis explores the geochemistry of near-surface groundwater above concealed kimberlite pipes using factor analysis to determine whether (1) a factor analysis can reveal an underlying structure (factors) in a multivariate groundwater geochemical dataset, and whether (2) those factors are related to the presence of concealed kimberlite. Factor analysis was performed on two datasets of nearsurface groundwater, collected at 0.2 m and 1.1 m below ground surface in peat. Results revealed that (1) there is a significant difference in the behaviour of elements in groundwater near the surface compared to those in deeper groundwater, which is sheltered from the effects of the atmosphere; (2) for both datasets, the first factor is dominated by elements known to be enriched in kimberlite, notably rare earth elements (REE), U, Th, Ti – the composition of factor one is consistent with their derivation from kimberlite in a limestone background where such elements are in very low concentration; (3) high-valence and lowvalence kimberlite indicator elements (KIE) are found separated into distinct factors suggesting that once released from the kimberlite after weathering, KIE are subjected to various geochemical processes to be differentiated as they migrate upward to the surface; and (4) Fe and Mn load on a factor distinct from other metals, suggesting that in this environment Fe-Mn-O-OH is not a significant controller of metal mobility in groundwater. Overall, this research has further highlighted the multivariate nature of geochemical processes in groundwater. Compared with previous work in geochemical exploration where often only univariate or bivariate statistics or single element profiles over concealed ore bodies were used, this thesis has shown that factor analysis, as a multivariate data analysis technique, is a robust exploration tool, able to shed light on relevant geochemical processes hidden within geochemical datasets. This thesis shows that high-valence KIE, notably U,V, Th, Ti and the REE, as a group, are better indicators of the presence of kimberlites than other well-known KIE. Single element concentration profiles such as Ni or Cr (known KIE) show similar anomalies over a concealed kimberlite as a factor score profile for factor one (U, V, Th, Ti, REE, Ni) would; however, it is the peculiar assemblage of elements in factor one that makes it unique to kimberlites, a feature that can be used in future exploration work for concealed kimberlites in similar surficial environments, such as the Siberian wetlands. The results suggest that future geochemical exploration work involving groundwater should focus on the more stable groundwater located below the zone of oxidation, sheltered from the effects of the atmosphere.