Toiyabe

Toiyabe

Posted on by Jim Tate

Location

The Toiyabe Property is situated in the northern Toiyabe Range, eastern Lander County, Nevada and it is approximately six miles southwest of Placer Dome’s Cortez Gold Mine and about 78 miles southwest of Elko, Nevada. Toiyabe consists of 86 unpatented, contiguous and unsurveyed mineral claims, totaling 1,776.76 acres. We estimate that approximately 31 acres (1.7% of the total) of the Toiyabe Property may belong to unrelated third parties.

History

Nevada ranks as one of the world’s most significant gold mining regions, with over 7.7 million ounces produced in 2004 and current reserves of approximately 64 million ounces. The vast majority of gold endowment and production occurs in northern Nevada along three major sediment-hosted gold trends; the Carlin Trend, the Battle Mountain Trend and the Getchell Trend. Significant production also occurs from epithermal deposits along the Northern Nevada Rift and Western Nevada Rift. The Toiyabe Property is located along the Battle Mountain Trend.

In the 1870’s a number of gold placer operations were put into production but these operations ceased due to poor recoveries and inadequate water supplies. However, in the early 1900’s there was a resurgence of mining activity in the Carlin and Crescent Valley area and the Gold Acres deposit was discovered on the north side of the Crescent Valley in 1910 and put into production in 1930. The Gold Acres deposit was the first sediment hosted “Carlin Type” disseminated gold deposit discovered in Nevada.

The proximity of the Toiyabe Property to the following or other documented gold and silver deposits does not suggest or indicate that the Toiyabe Property is similarly mineralized.

The Roberts Mountain Formation is an important lithological host to most of the gold deposits east of the Carlin Trend. In 1966 the United States Geological Survey outlined an extensive gold geochemical anomaly within silicified limestones of the Roberts Mountain Formation. In 1969 Placer Dome commenced further exploration in the Gold Acres area (located 12 miles to the north of the Toiyabe Property) and by 1973 Placer Dome had outlined additional reserves of 1.6 million tons grading 0.106 ounces per ton gold. Gold Acres mine was reopened and continued production until 1983. From 1984 to 1986 drilling was conducted over portions of the mine area and additional sulphide resources were outlined and mining activity resumed in 1986 and is still underway.

In 1986-87 Gold Fields Mining Corporation conducted limited exploration and drilling on the Pipeline property. Sub-economic gold values were intersected in some of the drill holes. The property was sold to Placer Dome and Kennecott (the Cortez Joint Venture) as a mill site for the Gold Acres mine. During condemnation drilling on Pipeline, significant gold mineralization was encountered including intercepts of 0.306 ounces per ton gold over 120 feet. The Pipeline and South Pipeline deposits are now in production. The newest and most significant discovery in the area is the Cortez Hills deposit, which was discovered in 2002. The Cortez Hills deposit is currently being drilled by the Cortez Joint Venture. The Toiyabe Property is located six miles south of the Cortez Hills discovery.

The Toiyabe mine was a small gold mining and heap leaching operation from 1987-1991 owned by Inland Gold & Silver Corporation. The Toiyabe mine has been abandoned and reclaimed; it lies on a claim block adjacent to and south of the Toiyabe Property. The mine processed approximately 2,300,000 tons of rock and produced approximately 89,000 oz of gold from three small pits. The Saddle deposit of the Toiyabe mine is a sediment-hosted, structurally controlled gold deposit primarily hosted by the Roberts Mountain formation but with the Roberts Mountain Thrust as the major control on the gold mineralization.

Historical Exploration

This section presents recent historical exploration activities on the total of the Toiyabe area. Work was conducted across the total area including the adjacent but off-site Toiyabe mine. Much of the history comes from summary documents that are reviews of material presented by Newmont in various reports over the years. Geochemical data predates NI 43-101 QA/QC protocols.

Exploration work was completed by Homestake (now Barrick), Getty Oil (now Energold Mining), Freeport Exploration (now Freeport-McMoran Copper & Gold Inc), Degerstrom Inc and Santa Fe Pacific Mining (now Newmont) during the period 1964-1991. Much of the work consisted of drilling. Other work completed by the various companies has been summarized in various documents that may or may not contain maps which would provide assistance in locating the various targets developed by the survey. In addition and more importantly, it is often difficult to determine how much of the previous work was completed within the current Toiyabe Property claim boundary as the claims were much different in 1964-1991. Therefore, in many cases brief summaries are all that remains of that work. Historical exploration includes:

  • approximately 10,000 regional and local stream silt samples were collected by Homestake in 1979
  • approximately 9,500 regional and local stream sediment samples were collected by Inland in 1988
  • airphoto and landsat studies
  • geological mapping
  • rock sampling by Inland and Freeport in the lower plate rock exposures
  • 6 square miles of soil surveys on 200 ft by 200 ft grid, 3 square miles of soil surveys on 400 ft by 400 ft grid were completed by Santa Fe in 1990
  • airborne magnetometer surveys were completed by Homestake in 1990
  • 4,165 rock chip samples were collected by Santa Fe in 1991
  • reverse circulation drilling of 159 holes on the current Toiyabe Property as part of a drill program consisting over 1,000 holes drilled in the area including the holes drilled to develop the nearby Toiyabe mine in 1979-1991
  • Bouguer gravity surveys over parts of the property were completed by Newmont in 1993

Geological Setting and Mineralization

The Toiyabe Property is hosted by a similar type of geological environment to the Cortez, Cortez Hills, Pediment, Horse Canyon, and Pipeline deposits, where a large window of lower plate Roberts Mountain formation occurs in the southern portion of the property.

Gold mineralization in the Toiyabe mine area occurs in the lower plate carbonates but also occurs in the upper plate siliceous sediments above the Roberts Mountain thrust fault. Little is known about the gold occurrences within the Toiyabe Property and much of the information in this section is derived from the historical gold occurrences at the Toiyabe mine. Despite the presence of numerous old prospect pits, there has been no recorded historic production from the Toiyabe Property. The proximity of the Toiyabe Property to the old Toiyabe mine does not suggest nor indicate that the Toiyabe Property is similarly mineralized.

At the Toiyabe mine, 60% of the gold is derived from the lower plate Roberts Mountain Formation while 40% of the gold comes from the upper plate package. The gold is fine grained and in a free state and is commonly liberated by heap leaching. The rocks are crushed and placed on the pads and dilute cyanide solution is sprinkled on the heaps. The pregnant solution is then collected and the gold (+ silver) is recovered by a series of carbon columns followed by stripping and electrowinning, overall gold recoveries averaged 65%.

Mineralized rock is commonly indistinguishable from the unmineralized rocks. Alteration in the mine area includes; silicification, decalcification, minor oxidization and remobilization of carbon. Gold is dominantly associated with silicification, either as quartz veins, quartz veinlets and/or replacement flooding. There is also an association with elevated arsenic, mercury, antimony and silver geochemistry which aids in the search for these deposits. Gold commonly occurs where narrow fracture systems intersect only certain sheared, permeable and reactive carbonates that result in larger, shear-breccia hosted gold systems. Additionally, significant zones of gold mineralization on the subject property are associated with lesser argillic alterations.

Gold in the Toiyabe mine is also associated with Oligocene aged rhyolitic-latitic dykes. In several areas of the mine, gold is found in quartz veins or siliceous flooding of igneous dykes, a common phenomenon in other mines in the Battle Mountain and Carlin gold belts. Insufficient mapping has been completed on the property to determine if similarly mineralized dykes exist on the Toiyabe Property.

Exploration

Approximately 159 near surface drill holes less than 400 feet deep have been conducted on the property, particularly during 1988 through 1991. This drilling has been interpreted to suggest variable potential for additional gold mineralization at identified target areas within a shallower hosting system.

A strongly mineralized fault zone with strong gold on surface sampling and down-hole drill intercepts demonstrate the potential of gold mineralizing fluids traveling from a deeper seated source to the recognized shallow mineralization. In conjunction with this is the fact that numerous deeper drill intercepts have low to moderate gold mineralization in erratic occurrences on the property.

The new hole drilled by Golden Oasis as well as many of the old 1988-1991 reverse circulation holes, confirmed the presence of the important lower plate stratigraphy, although further work is needed to determine if the lower plate rocks contain the right structural complexities and traps to host an economic gold occurrence.

Previously drilled holes are of limited depth typically in the 150 foot range with some drilled to 400 feet. This drilling presents a negative appearance to the ground but it is in fact encouraging because the amount of gold mineralization leakage in the near surface rocks is very encouraging for the potential of a deeper level gold system. Limited intercepts from deeper drilling and along known structures support the potential for deeper gold mineralization.

Mineralization, in economic quantities, is thought to occur at greater depths than has been drilled to date. This is demonstrated at the Cortez mine. The potential of the Cortez and Cortez Hills area only became clear when holes were drilled in excess of 1,000 feet. There could be several reasons for this but the main factor in all these deposits is believed to be the level at which “boiling” of hydrothermal fluids occurs and thus precipitate gold and silver.

Technical Report

Click here to view Toiyabe NI 43-101 Technical Report (May 27, 2009 PDF 4.6MB)

Toiyabe CSMT preliminary Interpretation
From: Frank P. Fritz, Fritz Geophysics
Date: 3 November 2006

The following is a brief review of the preliminary interpretation of the CSMT survey completed over a southern portion of the Toiyabe Project properties in central Nevada. This review is based on only the CSMT data and the anticipated geologic sections need to be added for a more complete interpretation.

Six lines of Controlled Source MagnetoTelluric data, CSMT, were collected on the southern end of the property over part of the current drilling program and over the most promising responses detected by the previous Tensor IP, TIP, survey from last year. The TIP data suggested a complex structural environment with large resistivity contrasts that may be associated with economic mineralization.

An ENE general cross section through the CSMT survey on Line 200N, included below, shows the typical vertical section interpreted from the CSMT data. The 2D model resistivities suggest a two layer case broken by several structures into a complex set of horsts and grabens but dominated by the grabens. The typical first layer from the surface is a very high resistivity unit while the second layer is a very low resistivity unit. The low resistivity second layer is not unusual for some of the rock types seen in Nevada but the very high resistivities are unusual for all of Nevada. The very low resistivities in the second layer limited the depth of penetration of the survey to less than 100m is some areas and probably less than 300m for most of the survey. Correlation between these resistivity layers and specific geologic rock types is not possible at this time.

The interpreted structures appear to be a set of very northerly and ENE directions. A plan view of the interpretation of the possible structures is included below. Over most of the survey area there is a thin layer, <100m, of higher resistivities over the low resistivity but in the interpreted graben areas the high resistivities dominate and could suggest a thicker section of the high resistivity unit, the grabens, or an increase in resistivity locally possibly caused by alteration.

Prioritizing exploration targets based on the resistivity data alone is not possible. The addition of any geological or geochemical data will be necessary to suggest drill targets. If the higher resistivities in the upper unit may caused by alteration then the highest resistivities are a priority target.

Frank P. Fritz
Fritz Geophysics