Exploration History at Grassy Mountain
Thirty years of high quality work by reputable operators have brought the Grassy Mountain Gold Project to its current advanced state.
The Atlas Era
In 1986 Atlas Precious Metals (Atlas) acquired the Grassy Mountain property from two independent geologists, Dick Sherry and Skip Yates.
Atlas recognized soil geochemistry as an important tool for locating buried hydrothermal cells at Grassy Mountain. Most of the Atlas exploration targets were identified by claim-corner (600’ X 1500’ grid) soil sampling anomalies. Atlas conducted detailed soil and float sampling on several anomalies and identified a genetic link between gold mineralization and silicification. Between 1986 and 1991, Atlas completed 403 drill holes totalling 221,500 ft. on the Grassy Mountain property. Out of the total, 193 were vertically oriented Reverse Circulation (RC) holes on 75 to 100 ft centers within the Grassy Mountain resource area. The remaining drill holes were located on prospects away from the main Grassy Mountain resource area. Many of these represent future exploration targets.
Atlas’ RC holes were drilled by Eklund Drilling Company from Elko, Nevada using Ingersoll Rand TH-60 and RD-10 truck-mounted drills with a nominal hole diameter of 5¼ inches. The RC cuttings were collected as five foot long samples. Twenty-two of the Atlas RC holes were drilled to at least 1,000 ft. in depth. Groundwater was reportedly not encountered above 750 ft., with the exception of some local perched water tables that were intersected along the northern portions of the deposit. Because the deposit is strongly silicified, drilling penetration rate was slow and resulted in excessive bit wear. Drilling along the main northeast structures was completed with some difficulty due to tight hole conditions and caving of rubble zones.
Atlas drilled ten core holes at Grassy Mountain to confirm high-grade mineralization identified by RC drilling methods, obtain samples for metallurgical testwork, and to collect geotechnical data. Two confirmation holes were drilled as NC and NQ angle holes by Longyear. Five core holes drilled specifically to obtain sample material for metallurgical testing were drilled as vertical PQ diameter holes by Boyles Brothers. Three geotechnical holes were also drilled by Boyles Brothers. Collar locations were surveyed by Apex Surveying from Riverton, Wyoming using a total station, and the holes were surveyed down-the-hole using an Eastman down-hole camera. Assay records indicate that the confirmation holes were sampled on interval lengths ranging from 0.5 to 7.5 ft. in length, with an average sample length of 4.5 ft. Whole core from the metallurgical holes was shipped to Hazen Research Inc. for metallurgical testwork, and the geotechnical holes were logged for various geotechnical parameters (e.g. RQD, fracture frequency, etc.).
Atlas expanded the original claim block and collected a wealth of geologic, mine engineering, civil engineering, and environmental baseline data to support a feasibility study, which was completed in 1990.
Declining gold prices and the perception of an unfavorable permitting environment at that time discouraged Atlas from developing the project, and the property was optioned to Newmont Exploration Ltd (Newmont) in 1992.
The Newmont Era
Newmont leased the Grassy Mountain property from Atlas in September 1992 for US$30 million. In 1993, Newmont geologists mapped 40 square miles at a scale of 1:6000 and collected approximately 2,600 soil samples on a 400-ft by 200-ft grid to identify anomalies missed by the coarser Atlas grid. During 1993 and 1994, Newmont collected more than 400 rock chip samples and conducted several geophysical programs. A ground-based gravity survey was carried out along roadways and airborne magnetic and radiometric surveys were flown over the entire property. Ground based gradient array and ground magnetic surveys were conducted over primary target areas.
Newmont initiated an eleven-hole (11,472 ft) inclined diamond core drilling program designed to intersect and define the geometry of potential high-grade gold zones. Additionally, Newmont drilled one wedge hole off of their initial core drill hole. Three additional holes (2,912 ft) were drilled as RC pilot holes with core tails. Drilling was completed by Longyear. All of the holes were drilled as HQ diameter, with the exception of four holes which had to be reduced to NQ size due to ground conditions. Down-hole surveys were conducted by Scientific Drilling.
Newmont’s angle core program intercepted several high-grade (> 0.10 opt) gold zones within an area measuring 600 ft long by 350 ft. wide by 250 ft. thick. Mineralization was constrained to the northeast by a single hole which failed to encounter intercepts in excess of 0.10 opt. Newmont considered the western extent of the main high-grade zone effectively closed off after encountering only low grade gold (0.012 – 0.019 opt) and local barren quartz-chalcedony veins.
In late 1994, Newmont drilled 15 holes totalling 15,009.5 ft. and completed a mineral resource estimate that became the basis for an economic and mining method evaluation that was completed in 1995. Newmont determined that the project did not meet corporate objectives and returned the property to Atlas in September 1996.
The Tombstone Era
In January 1998, Atlas granted Tombstone Exploration Company Ltd (Tombstone) the option to purchase 100% of the property. Tombstone executed the option agreement and conducted an exploration program which included eight reverse circulation and two core holes totalling roughly 8,072 ft.
Prior to finalizing their agreement with Atlas, Tombstone completed an extensive review of previous work at the property and commissioned an economic study of alternative development scenarios. Relying heavily on Newmont’s gradient array surveys to define potential targets, Tombstone initiated a 10 hole drilling program that totalled 8,072 ft of reverse circulation and core drilling. Dateline Drillingperformed all of Tombstone’s RC drilling, and diamond core drilling was completed by Ray Hyne Drilling. Down hole surveys were reportedly conducted by Silver State Surveys using a gyroscopic survey tool, but no written records are present in Calico’s archives. However, the survey measurements in the historic drill hole database indicate that the drill holes did not deviate to any significant degree.
Lack of venture capital forced Tombstone to return the property to Atlas in May 1998.
The Seabridge/Calico Era
In February 2000, Seabridge Gold entered an option agreement with Atlas to acquire a 100% interest in the Grassy Mountain property. Seabridge completed its acquisition of the Grassy Mountain Project in April 2003, and in April 2011, signed an option agreement granting Calico Resources the sole and exclusive right and option to earn a 100% interest in the project.
During the 2011 exploration program, Calico mapped and sampled the Grassy Mountain deposit and completed three core and nine reverse circulation drill holes in the primary zone of mineralization on the property. Calico’s exploration strategy was to target areas where resource expansion was most probable. Historical data was thoroughly reviewed prior to drilling, and fresh sets of cross-sections and long-sections were constructed based on existing information. New interpretations of the orientation of mineralization and geology were plotted on the new sections. The new sections were then used to select areas where in-fill drilling was needed and areas where gold mineralization was open-ended and resource expansion probable. A detailed geologic model was produced based on the results of the 2011 exploration work, and subsequent supporting geophysical surveys were completed in March, 2012.