Best Chance
Explore copper skarn mineralization exposed along the Copper Haul Road.
Site Introduction
Location of the Best Chance deposit and Grafter Extension showing along the Copper Haul Road.
Location:
60.492741°, -135.123357° (latitude/longitude)
Overview:
The Best Chance claims were staked on July 7, 1899, and were originally named Last Chance because the prospector (Angus McKinnon) did not think there would be much value to the site. The name was changed to Best Chance in July 1900, after initial results proved encouraging.
Mineralization at the Best Chance deposit comprises chalcopyrite and bornite in a massive magnetite-serpentine skarn. The skarn body forms a series of hummocky hills east of the Copper Haul Road. A small amount of underground mining took place in ~1907, with a very limited amount of production of high-grade ore. This was followed by exploration drilling and geophysical work from the 1950s up until the early 1990s.
This field trip also includes the Grafter Extension outcrop, which is just across the Copper Haul Road from Best Chance. Grafter Extension shows all three major rock types in the Whitehorse Copper Belt: limestone, granodiorite, and skarn.
Overview Video
Join Yukon University geologist Dr. Joel Cubley for a brief overview of the rock types and mineralization at the Grafter Extension outcrop.
Virtual Field Trip
Now you can explore the field site using a Kuula virtual trip! Click anywhere on the site tour to launch it, then make sure to click the full-screen button in the top right corner to get the full experience. Once in the tour, click on individual sites to zoom in further and interact with the site.
Grafter Extension Outcrop
The Grafter Extension outcrop is a fantastic place to see the geologic relationships between limestone, granitic intrusive rocks, and skarn that form along the intrusive contact. Explore the outcrop further below!
Geologic Relationships
There are three main rock types at the Grafter Extension outcrop: limestone, granodiorite, and magnetite skarn.
Granodiorite
Rock Description:
- Granodiorite is a coarse-grained intrusive igneous rock which crystallizes slowly from magma kilometers beneath the Earth's surface.
- The granodiorite here is made up of the minerals hornblende, plagioclase, potassium feldspar, biotite, quartz and magnetite.
- Near the intrusive contact with limestone, secondary minerals have formed within the granodiorite including epidote, diopside (clinopyroxene), actinolite, and copper sulfides.
Click on a 3D sample of Grafter Extension granodiorite to further explore its mineralogy and textures.
The coarse black minerals are predominantly hornblende, with some minor biotite. The light-colored white, pink, and gray minerals are plagioclase, potassium feldspar and quartz, respectively. Green minerals are secondary chlorite and epidote alteration.
Texturally, this rock is coarse-grained (phaneritic) and equigranular.
Magnetite Skarn
Rock Description:
- Magnetite skarn is abundant at Grafter Extension, localized along the intrusive contact between granodiorite and limestone. This skarn contains the iron-oxide mineral magnetite, the copper sulfide minerals bornite and chalcopyrite, and small amounts of pyrite. Other minerals in the rock include serpentine, garnet, diopside, and tremolite.
- The copper sulfide minerals have locally been altered by weathering into secondary copper minerals like malachite and chrysocolla (both green), and azurite (blue).
Click on the 3D sample of Grafter Extension magnetite skarn to further explore its mineralogy and textures.
Limestone
Rock Description:
- The limestone at this site has been recrystallized into coarser-grained marble that ranges from white to gray in colour.
- Close to the contact with the granodiorite, the limestone contains metamorphic minerals including pyroxene, amphibole, and andradite garnet, as well as small amounts of serpentine. These metamorphic minerals formed in the limestone due to the high amounts of heat and fluids added by the magma.
- There are also abundant quartz veins near the contact, where fluids from the magma body traveled into the limestone along joints in the rock.
Click on the 3D sample of Grafter Extension limestone to further explore its mineralogy and textures.
Mineralogy
There are a wide array of minerals to discover at Best Chance. Confident in your mineralogy skills? Hover over the "i" icon to reveal what each mineral is.
Mineral samples from the Earth Sciences teaching collection at Yukon University.
Digital Terrain Model
Interested in interacting with the site in a full 3D format? Check out the digital terrain model with orthoimagery below. Navigation within the model can be achieved either with a mouse or using tablet touch-commands. The model is large, and can take several minutes to load depending on your computer and internet connection. We recommend expanding it to full screen. The experience is worth the wait!
