A mineral assessment of the Tombstone study area was undertaken by the Department of Economic Development in the summer of 1998 at the request of the Department of Renewable Resources. The purpose of the mineral assessment was to produce a mineral potential map, which was to be used to assist with the finalization of the boundaries of the Tombstone Territorial Park. Following an initial compilation, a field program was designed to document known mineral occurrences, test and improve the existing regional mapping, investigate geochemical anomalies, characterize favourable environments for mineralization, sample for lithogeochemistry, and prospect for mineralization. A field program resulted in the discovery of several new mineral occurrences, as well as the discovery of previously unmapped geological formations. Fieldwork was followed by a compilation phase that integrated the new information to the existing geoscientific data. The geology of the study area was subdivided into thirteen geological tracts. A panel of five industry and government experts, familiar with the geology, mineral occurrences and mineral deposit types to be found in the area, was convened in June 1999. Based on the final compilation and their expertise, they produced a relative ranking of all the tracts according to their potential to host mineral deposits, from highest potential to lowest. The highest-ranking tracts are those that include, or are near the Cretaceous intrusions (Tombstone, Mount Brenner and smaller intrusions) and have strong potential for intrusion-hosted (Fort Knox-type, porphyry uranium, skarn) and intrusion-related (skarns, veins, replacement) mineralization. Other tracts demonstrate potential for Wernecke Breccia, shale-hosted nickel sulphide, ultramafic-hosted nickel and listwaenite, Carlin-type, Mississippi Valley-type or replacement lead-zinc, as well as volcanogenic mineralization. A final boundary was adopted in December 2000; it includes land outside of the original study area. This final boundary therefore includes areas that were not assessed in this study. All our wildlife sightings were documented and were included in the subsequent wildlife survey.

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This outreach product includes simplified geology of the Tombstone area.

The Len porphyry gold prospect is located 47 km north of Mayo, Yukon, in the Tombstone Suite intrusive belt. The area was explored as a Keno Hill-style silver prospect in the 1960s and 1970s. An arsenic-in-soil anomaly first identified in 1980 was followed up by soil geochemistry and excavator trenching in 1996. Multiple sheeted quartz-sulphide veins hosted in a previously unmapped granodiorite stock were discovered during the trenching program. A six-hole program of diamond drilling in 1997 encountered grades ranging up to 2.22 g/t gold across 18.6 m, and showed that gold mineralization is dominantly within, but not restricted to, the intrusive stock.

The study area is centred on the 91.2 ± 0.9 Ma Scheelite Dome quartz-monzonite stock of the Tombstone Plutonic Suite (TPS). This stock and associated dykes and sills intrude highly deformed metasedimentary strata of the Yusezyu Formation of the Neoproterozoic to Lower Cambrian Hyland Group. The emplacement of TPS intrusions post-dates regional greenschist-facies metamorphism and multiple phases of ductile deformation related to the Tombstone strain zone. Although the Scheelite Dome stock hosts auriferous, sheeted quartz veins, extensive soil geochemistry indicates that the bulk of the gold resource is hosted in the variably hornfelsed metasedimentary rocks immediately south of the stock. The associated gold-in-soil anomaly forms an east-trending corridor of anomalous gold values (>80 ppb) approximately 6 km long by 1.5 km wide, with a more weakly defined eastern continuation. Where metasedimentary bedrock is exposed in the corridor, gold is hosted in fault-vein arrays, and less commonly as disseminated grains and in replacement zones. The styles and distribution of mineralization are largely controlled by brittle structures; a phase of east-west shortening was largely coeval with gold mineralization. R-mode factor analysis of multi-element geochemical data indicates two geochemically distinct metal suites within the area of the gold-in-soil anomaly at Scheelite Dome. The first suite, characterized by Au-Te-Bi ± W ± As, possesses the stronger gold association and is typical of intrusion-related gold occurrences elsewhere in the Tombstone gold belt. The second suite displays a metal association of Ag-Pb-Zn-Cd-Sb ± Cu ± Au, which is more characteristic of mid-Cretaceous Ag-Pb-Zn mineralization in the Keno Hill district, located approximately 60 km to the east-northeast. Field observations, combined with soil geochemistry, suggest that the different metal associations are paragenetically related. However, the possibility of two distinct hydrothermal events cannot yet be ruled out.

The Cynthia property overlies a large (greater than 2x2 km) area of gold mineralization related to a Cretaceous Tombstone Suite quartz monzonite intrusive body. The mineralization is controlled by two district-scale fault zones and is especially intensive in the area of their intersection, located above and adjacent to the intrusive body. These larger structures host abundant gold-bearing massive and drusy quartz and chalcedony veins, zones of intense stockwork and strong brecciation, as well as numerous mineralized felsic dykes. The gold grades within the mineralized structures are commonly in the range of 200 ppb to 2.0-3.0 g/t Au, with higher (up to 16 g/t Au) values attributed to the fault intersection area. Multi-staged gold mineralization found in the quartz veins, stockwork and altered dykes is associated with sulphide minerals (mainly pyrite and arsenopyrite) and elevated As, Bi and Ag values. A later mineralizing episode produced sulphide mineral-bearing chalcedony and drusy quartz veins, with gold concentrations accompanied by elevated Sb, Hg, Ag and Pb values, indicating the affi nity of epithermal style gold mineralization. The property is considered to represent a bulk-tonnage exploration target, with potential of the structures to host a major gold deposit. During the 2002 exploration program, the prospect has been advanced to a drill-ready stage.

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A copy of this thesis is available at the EMR library – QE376.5.Y8 R39.

A mineralogical study was conducted by the Applied Mineralogy Group on a niobium-bearing rare earth ore from the Lancer deposit in Yukon as a cost recovery project for Mr. Dodge, President Dodgex Ltd. The study was conducted in two parts. One part is to identify the minerals and to determine the compositions and modes of occurrence of rare earth minerals, and the second part is to determine the relative quantities of the rare earth minerals and to determine their liberation characteristics.