Blachford Property
Overview
The Blachford Property currently consists of one mineral claim encompassing 7000 acres in south-central Northwest Territories. The Property is located some 95 km southeast of Yellowknife, north of the East Arm of Great Slave Lake.
The Blachford Property is within the Precambrian Shield, within the Aphebian alkalic, plutonic Blachford Lake Complex (BLC). The BLC is an igneous domain, in which successive intrusive phases range from older mafic bodies, through intermediate intrusions, to alkali-rich and increasingly felsic plutons. The Blachford Property is situated within the youngest Grace Lake Granite domain, near the centre of the BLC, south of Blachford Lake and north of Thor Lake. The Grace Lake Granite appears to be a more felsic contemporaneous equivalent of the Thor Lake Syenite.
Nepheline syenite outcrops in the central sector of the BLC, in the environs of Thor Lake, contain rare earth element (REE)-rich mineralization. What is now known as the Nechalacho REE-Zr-Nb-Ta Deposit (formerly the Thor Lake Deposit) is hosted by a subhorizontal, layered nepheline syenite body situated below the uppermost Thor Lake Syenite-Grace Lake Granite lithologies of the BLC. In 2010, the hydrothermally altered REE-Zr-Nb-Ta-bearing nepheline syenite intrusion was shown not to be confined to the environs of Thor Lake. It is now thought that this REE-rich layered intrusion, the Nechalacho nepheline syenite, is a larger sill-like entity with lateral extensions to the north around Cressy Lake and perhaps even beyond that point.
Two sites (Localities 1 and 2) were visited based on aeromagnetic anomalies identified by the GSC (1988) and geological investigations were performed. The Grace Lake Granite outcrops examined had crosscutting fractures and narrow veins (<2m) that often weathered to a chocolate-brown colour and often proved to be radioactive (scintillometer readings of up to 650 cpm). The occasional medium-grained aplitic lithologies encountered on the author's cursory ground surveys were also slightly radioactive. Many of the brown weathering fractures and narrow veins were clearly enriched in U±Th and possibly originally contained sulphides. Six samples of these veins and their altered wall rocks were collected, together with one background sample of pristine Grace Lake Granite.
The altered Grace Lake Granite and veins contain significant introduced contents of Zr, Nb, Ta, Th, and U with lesser but significant quantities of light rare earth elements (LREE) La, Ce, Pr, Nd, Sm, and heavy rare earth elements (HREE) Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, and Y. Total rare earth element oxides (TREO) within the veins show a maximum of 0.126%; heavy rare earth element oxides (HREO) are 21.99% of the TREO in this sample. This ratio is almost the same as the HREO distribution recorded by Avalon for the Basal HREE zone of the Nechalacho Deposit below Thor Lake, where average HREO content is about 20% of the TREO content (Avalon Rare Metals, 2011). Percentage-level concentrations of Nb2O5 in three samples are highly significant. The contents (up to 0.455%) compare with average concentrations of Nb2O5 in the Nechalacho Syenite REE-Zr-Nb-Ta-(U-Th) Deposit around Thor Lake to the southeast.
Subsequent structural interpretation of satellite images of the Blachford Property has revealed a series of topographic lineaments that could have resulted from uplift or roof collapse of an underlying younger intrusive body. These lineaments are parallel to NW-trending anisotropic features visible on a preexisting aeromagnetic data map (magnetic highs) and on an airborne radiometric survey (Th equivalent). This has led the author to hypothesize that the REEZr-Nb-Ta-bearing Nechalacho nepheline syenite intrusion could extend northwestward from Thor Lake at depth to the Blachford Property. The newly discovered Zr-Nb-Ta-Th-U-REEbearing veins may be caused by upward venting of hydrothermal fluids from an underlying REEZr-Nb-Ta-(U-Th)-enriched intrusion. Thus, to test the hypothesis of the possible existence of REE-Zr-Nb-Ta-bearing Nechalacho nepheline syenite below the cover of Grace Lake Granite on the Blachford Property.
The Blachford Property is considered under-explored for syenite-hosted REE-Zr-Nb-Ta deposits and is of sufficient merit to warrant further exploration.
The Blachford Property is within the Precambrian Shield, within the Aphebian alkalic, plutonic Blachford Lake Complex (BLC). The BLC is an igneous domain, in which successive intrusive phases range from older mafic bodies, through intermediate intrusions, to alkali-rich and increasingly felsic plutons. The Blachford Property is situated within the youngest Grace Lake Granite domain, near the centre of the BLC, south of Blachford Lake and north of Thor Lake. The Grace Lake Granite appears to be a more felsic contemporaneous equivalent of the Thor Lake Syenite.
Nepheline syenite outcrops in the central sector of the BLC, in the environs of Thor Lake, contain rare earth element (REE)-rich mineralization. What is now known as the Nechalacho REE-Zr-Nb-Ta Deposit (formerly the Thor Lake Deposit) is hosted by a subhorizontal, layered nepheline syenite body situated below the uppermost Thor Lake Syenite-Grace Lake Granite lithologies of the BLC. In 2010, the hydrothermally altered REE-Zr-Nb-Ta-bearing nepheline syenite intrusion was shown not to be confined to the environs of Thor Lake. It is now thought that this REE-rich layered intrusion, the Nechalacho nepheline syenite, is a larger sill-like entity with lateral extensions to the north around Cressy Lake and perhaps even beyond that point.
Two sites (Localities 1 and 2) were visited based on aeromagnetic anomalies identified by the GSC (1988) and geological investigations were performed. The Grace Lake Granite outcrops examined had crosscutting fractures and narrow veins (<2m) that often weathered to a chocolate-brown colour and often proved to be radioactive (scintillometer readings of up to 650 cpm). The occasional medium-grained aplitic lithologies encountered on the author's cursory ground surveys were also slightly radioactive. Many of the brown weathering fractures and narrow veins were clearly enriched in U±Th and possibly originally contained sulphides. Six samples of these veins and their altered wall rocks were collected, together with one background sample of pristine Grace Lake Granite.
The altered Grace Lake Granite and veins contain significant introduced contents of Zr, Nb, Ta, Th, and U with lesser but significant quantities of light rare earth elements (LREE) La, Ce, Pr, Nd, Sm, and heavy rare earth elements (HREE) Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, and Y. Total rare earth element oxides (TREO) within the veins show a maximum of 0.126%; heavy rare earth element oxides (HREO) are 21.99% of the TREO in this sample. This ratio is almost the same as the HREO distribution recorded by Avalon for the Basal HREE zone of the Nechalacho Deposit below Thor Lake, where average HREO content is about 20% of the TREO content (Avalon Rare Metals, 2011). Percentage-level concentrations of Nb2O5 in three samples are highly significant. The contents (up to 0.455%) compare with average concentrations of Nb2O5 in the Nechalacho Syenite REE-Zr-Nb-Ta-(U-Th) Deposit around Thor Lake to the southeast.
Subsequent structural interpretation of satellite images of the Blachford Property has revealed a series of topographic lineaments that could have resulted from uplift or roof collapse of an underlying younger intrusive body. These lineaments are parallel to NW-trending anisotropic features visible on a preexisting aeromagnetic data map (magnetic highs) and on an airborne radiometric survey (Th equivalent). This has led the author to hypothesize that the REEZr-Nb-Ta-bearing Nechalacho nepheline syenite intrusion could extend northwestward from Thor Lake at depth to the Blachford Property. The newly discovered Zr-Nb-Ta-Th-U-REEbearing veins may be caused by upward venting of hydrothermal fluids from an underlying REEZr-Nb-Ta-(U-Th)-enriched intrusion. Thus, to test the hypothesis of the possible existence of REE-Zr-Nb-Ta-bearing Nechalacho nepheline syenite below the cover of Grace Lake Granite on the Blachford Property.
The Blachford Property is considered under-explored for syenite-hosted REE-Zr-Nb-Ta deposits and is of sufficient merit to warrant further exploration.