Summary:
Deposit Types
At Chandalar, both lode and placer gold exist within the district. The placer deposit is the focus of this report, but a significant exploration potential exists to find and develop the lode deposits that were the source of the placer deposit.
Lode Deposits
Lode gold occurs throughout the Chandalar property in definable systems of veins, veinlets, disseminations, and auriferous lenses of quartz within or adjacent to northwest-trending shear zones.
The schist-hosted Mikado mineralization occurs in discontinuous elongate lenses and veins that pinch and swell as border zones of stockwork and sheeted veinlets. The Mikado shear zone, generally found in the hanging wall, contains the majority of the mineralization. Recurrent movement along the shear explains the discontinuous nature of the mineralization, the pulverization of quartz to a clayey sugary texture, and the numerous ragged inclusions of host rock.
Elsewhere, veins such as the Little Squaw, Crystal, Kiska, Prospector, and Grubstake are hosted in splay faults and are more competent and continuous and mineralization primarily occurs as pods and ore shoots. Overall, auriferous and subparallel quartz veins of the Chandalar district occur across a five-mile width and a northwest-trending four-mile strike length.
Placer Deposits
Placer gold in the Chandalar Mining district was liberated from lode sources of the former highland weathering surface that rose more than 3,000 feet (914 meters) above the surrounding lowlands during several episodes of erosion and concentration and was further complicated by repeated advances of Quaternary glaciation from the north. Subsequent downcutting on each glacial retreat occurred in response to newly established base levels along the wide valleys to the north and west of the district. These glacial events scoured the upper placer streams of Tobin, Boulder, Woodchuck, McLellan, and Big Squaw Creeks but did not destroy pre-glacial pay streaks at the lower valleys of Little Squaw, Tobin (above Woodchuck Creek), and probably not Big Squaw and McLellan Creeks. These pre-glacial placer deposits were preserved during glaciation, and significant targets remain.
The complex glacial-fluvial history of the Chandalar region formed placers and placer exploration targets that exhibit several differing deposit types. On the north and east side of the district, the placers are a combination of stacked sequences of normal fluvial and glaciofluvial channel deposit that have formed in second order streams and feature bedrock and false bedrock pay channels. On Little Squaw Creek, and possibly on Big Squaw and Nugget Creeks, resistant bedrock along the north margin of the hills has influenced rapid stream gradient changes that created ancestral canyons below which paleo-fluvial and modern glaciofluvial fans have formed.
The later type is formed by combined fluvial and glaciofluvial processes and is deposited on glacial falsebedrock. These processes result in deposition of significant thickness of auriferous sediment as exhibited at Little Squaw Creek and possibly within other drainages along the north side of thedistrict.
This deposit is geologically characterized as an aggradational placer gold deposit. The plan view of the Chandalar Mine deposit is somewhat funnel-shaped, and because of this has beendivided into two distinct geomorphological zones: the Gulch, or narrower channel portion, and the Fan, or broad alluvial apron portion.
Mineralization
Lode Mineralization
Most high-grade mineralized zones within vein systems are less than 150 feet long and 2 to 10 feet wide. Vertical extents are unknown but probably exceed 200 feet. Individual prospects discovered at various points along major shear zones were originally thought to be discrete discoveries, but groups of prospects have since been determined to be related along a common structure.
Placer Mineralization
Placer gold occurs within the pre-glacial fluvial, interglacial glaciofluvial, and post-glacial fluvial, permafrost deposits on Little Squaw Creek. The gold is coarse, crystalline, and bright, indicating that it was transported only a short distance from its sources. Small nuggets are common, and there is little finegrained gold (-80 mesh). Quartz inclusions and attachments are common on gold particles but make up only a few percent by volume.
The pay streak on Little Squaw Creek is subdivided into the “canyon” placer upstream of a bedrock constriction underlying Lines 4.8 through 6, and an “alluvial fan” placer downstream of the buried constriction that extends at least as far north as Line 1.2., a distance of about 2,000 feet. Fluvial gravel hosting the placer is mostly composed of gray to black chloritic schist, which is commonly seen in the surrounding hills. Gold-bearing gravels composing the alluvial fan range from 15 to 137 feet thick and average 80 feet thick over a width of up to 1,262 feet. The pay streak within the fluvial gravel on the canyon section varies from 50 to 136 feet thick over a width from 240 to 570 feet. The placer deposit is open to further mineralization to the east, west, and north.
Overburden on the fan is composed of frozen, clay-rich glacial till. Ice is moderately abundant in the overburden of the alluvial fan and may compose 10% of the total volume. Ice is particularly prevalent under the western end of Line 1.2, where it forms massive lenses 15 to 20 feet thick in Hole 18. Thawing ice appears to be responsible for the actively subsiding thermokarst pond east of the road. The barren till overburden averages 65 feet thick. Overburden on the canyon placer is mixed glaciofluvial sediments and can carry minor concentrations of gold at the surface and disseminated throughout. The overlying barren sections have a highly variable thickness, ranging from 0 to 75 feet with a 41-foot average.