|...Starting with first principles...
|America First Trust financial services
|...Investment advice and management for uncertain times...
Source: Nevada Pacific Gold
f) Carlin deposits can exist at a variety of depths and in a wide variety of shapes. Some Carlin mines are still finding gold down to 6,500 feet below the surface with no end in sight, at grades of 1 to 1.5 oz a tonne. Grades actually tend to improve with depth. .As a countervailing factor, at greater depths miners also tend to encounter ores with higher sulfur content and other "refractory" characteristics that make leaching gold out of ore more expensive. Conversely, weathering or "oxidation" of ores near the surface makes them easier to process.
Carlin gold deposit structures can be narrow and angle vertically towards the surface rather than lie on a horizontal plane. Some Carlin deposits that have become very lucrative to miners are only about 100 to 400 feet wide in areas and start over 300 feet below the surface. Exploration programs can easily miss them without saturation drilling.
Some other important general observations.
The major faults are often very old, some going back over several hundred million years. Many are very deep, penetrating over 20 km down into the earth's crust. Some geologists told me it would be a crude, but not bad analogy to compare the San Andreas Fault in California today with the Carlin and Cortez fault systems that existed over 100 million years ago. Currently gold deposits and other forms of mineralization are forming around hot springs near the southern end of the San Andreas fault at the Salton Sea in Southern California. Further south along the San Andreas Fault one finds the Mesquite open pit mine, which has produced millions of ounces of gold.
With a few small exceptions, none of the major Carlin faults or Cortez faults are obvious from the ground or by aerial pictures or satellite reconnaissance, having been covered over by many events in relatively recent geological history, to include volcanic activity and the creation of cross rifts.
Most Carlin-style gold deposits resulted from an upward thrust of gold-bearing fluids roughly 38 million years ago into northern Nevada. As discussed in Part Two, this geologic event coincided with the end of a several hundred million year tectonic plate compression cycle and also a counter clockwise rotation of the Pacific Plate that changed the direction of the Hawaiian Island chain.
Dr. Snyder pointed out that the 38 million year mark actually involved a huge pulse surge, as if in a statistical cluster function. However, Carlin-style deposits have actually been formed in many other geological ages as well. The Willard Gold Mine by Lovelock, NV has a 600,000 year old Carlin deposit. The Hycroft Mine at Sulphur, NV has a 4 million year old deposit. At the other end of the scale, deposits at the Goldstrike Mine on the Carlin Trend go back 120 million years. This reinforces the idea that it can pay to be in area that has had gold formation characteristics for many different geological ages in order to offer numerous possibilities for "reactivations" of structures.
Dr. Snyder also pointed out that there is a wide geographic dispersion of Carlin-style sites across northern Nevada, to include places in Utah. He feels that it is absurd to think that Northern Nevada has been over-explored. At this stage he does not know if Cortez will end up being bigger than Carlin. He also does not know if some other mineral belt in Northern Nevada could wind up being bigger than either Carlin or Cortez. He believes that there is definitely a lot more opportunity ahead.
Last, but not least, the Carlin Trend consists of more than just isolated deposits. In the view of John Leask, Chairman of White Knight Resources, it reflects a major gold field. As gold bearing fluids rose to the surface, they became trapped under Upper Plate structures and formed deposits, analogous to the way oil and gas fields form pools underneath anticline traps. In fact there are carbonaceous anomalies surrounding certain gold deposits that lead many geologists to believe that oil or gas were also once trapped in the same area. Later these hydrocarbons got cooked off into graphite.
FAULT-CENTRIC THEORISTS AND THE SEARCH FOR THE LOST CONTINENTAL SHELF
As noted in my discussion of White Knight Resources in Part Four, its geophysicist, Hans Rasmussen, once worked for Newmont Mining to find deposits along the Carlin Trend. He would often hear the slogan, "If you are out of the Fault, you are out of the game." Hence, finding the Cortez Fault system has been White Knight's foremost objective.
Mr. Rasmussen believes that the Cortez Fault system has been the super highway that has brought gold-bearing fluids from very deep in the earth towards the surface. White Knight views the Cortez Fault system as part of an extremely old continental shelf structure. Interestingly enough, a Jan 2005 Placer Dome presentation has a slide showing the Australian continent rifting away from western North America, to include central Nevada, somewhere between 900 to 700 million years ago (Timmons, et al, Feb 2001 GSA Bulletin). In this slide, the edge of North America runs through north central Nevada.
The picture above shows White Knight's concept regarding where the main Cortez Fault system lies. However, the location of the fault system is still the subject of considerable conjecture.
According to Brian Kirwin, President of American Bonanza, one can find an exposed sheet of breccia the length of a football field south of the Cortez Mine that reflects an outcropping of the Cortez Fault system. This was exposed by miners as a result of blasting. However, for the most part, the Cortez Fault system lies concealed underground. As discussed in Part Two, much of the topography you see on a topographical map, which is the same that you would see driving through the area today, was created by dropping valley floors of the Basin and Range in the last 20-30 million years as the western U.S. has started its stretch or "extension" cycle. The crack lines that define the valleys that parallel mountain ranges were probably created during the preceding approximately 350 million year long compression cycle, as I will discuss later.
White Knight's portrayal of the Cortez Fault system theorizes that the Cortez Fault makes a pivotal break between the Pipeline Complex and the Cortez Hills discovery area in the central Cortez Joint Venture area. The Pipeline Complex and Cortez Hills discovery are about 14 km or 8.7 miles apart. Crescent Valley, filled with alluvium, lies between these two deposits. The northern stretch may be anchored in the south by the Pipeline Complex. It may angle northward at about 10 degrees northwest. The southern stretch may be anchored in the north by the Cortez Hills discovery, and move diagonally in a SSE direction.
The NNW Main Fault School and Supporting Structures
Interestingly enough, as we start at the Pipeline Complex and work our way SE and then SSE, we see ample evidence of "supporting structures" strongly associated with the Cortez Trend Fault system. It is worth reviewing some of this evidence from such sources as Placer Dome, J-Pacific Gold, and American Bonanza.
The illustration below from Placer Dome's September 2004 Technical Report shows the presence of parallel "controlling structures" angling towards the Cortez Hills discovery. Hans Rasmussen of White Knight believes that this is none other than the Cortez Trend Fault system.
Source: Figure 10-2: Cortez Hill Deposit and Gravity Anomalies from the September 2004 Placer Dome Technical Report. This provides "ounce-foot" data, with the following grade and thickness key: Gray 1-2, Blue 2-5, Yellow 5-10, Green 10-25, Orange 25-50, Red 50-100, Magenta 100-200, Purple 200-300, Pink >300.
|The report "The Golden Trend Project of J-Pacific Gold Inc." by geologist David R. Shaddrick shows how very definite fault structures exist SSE of the Cortez Hills discovery. Below I provide an interpretive geological map and a cutaway "cartoon" provided in his report:
Please note in the illustration above the Northern Nevada Rift running SSE down the east side of the property (discussed later). In addition, there are not one, but two separate faults running down the western side marked "Cortez Fault 1" and "Cortez Fault 2." According to Mr. Shaddrick, the existence of these faults is well documented. In fact, he said that he would amazed if another paralleling Cortez Fault did not lie further to the west, possibly running through the NDT Ventures property.
Please note that the"cartoon" above, like the preceding illustration, shows the two Cortez faults and also NE trending faults running in parallel. Later I discuss the "Northeast Fault School." These faults tend to run parallel to the mountains and valleys created in more recent geological history. Curiously absent from these illustrations are WNW faults running in parallel to each other that I also discuss later.
Incidentally, the cartoon above also shows "ore bodies" in pink. Mr. Shaddrick emphasized that the "ore bodies" are hypothetical only, and that geologists frequently engage in conjecture from sketchy data. As a caveat for investors, the existence of faults do not guarantee gold mineralization, and there is always a chance that J-Pacific will never find economic gold deposits on its Golden Trend property.
Looking further south, we also see some interesting fault structures running in parallel in the area of American Bonanza's Gold Bar Mine. In my recent phone conversation with Brian Kirwin, American Bonanza's CEO, he felt that there is a strong probability that the southern end the Cortez Fault system runs through the Gold Bar mine, as indicated by the red line marked "Ore Controlling Fault" in the map below. Even if it turns out this could be a splay and not the main fault, he still believes that American Bonanza's property is very likely adjacent to if not right on top of the fault system.
Source: American Bonanza
The American Bonanza map above also depicts horst blocks, which can be indicative of being next to a major fault. Incidentally, Mr. Kirwin worked for Placer Dome from 1990 to 1997. He discovered the Rooster Deposit on BacTech's property, drilled the Hilltop Mine area, and ranks among the most seasoned exploration geologists in the Cortez Trend area. He happens to agree with White Knight that the main fault system very likely runs up north through the Hilltop Slaven area. But he also pointed out that it can be hard to find deposits that might lie over 500 feet under ground in sometimes thin and high angle formations, and reminded me that there could be some significant segments on the Cortez Trend map where no economic gold deposits may ever be found.
ALTERNATIVES TO SHOT GUN DRILLING
How do we uncover the location of the ancient fault system lying beneath more recently created mountains and valleys without having to drill out the whole area? White Knight has developed a gravity map that incorporates U.S. Geological Survey data. However, it is proprietary and currently not available to the general public. The company believes that this map shows the outline of the Cortez Fault system. The gravity map was shown as part of Mr. Rasmussen's Dec 10, 2004 presentation at the Northwest Mining Association Technical session. I also gave a presentation during this same technical session, albeit on a different topic, and have seen this map.
Below I have reproduced a reasonably similar map publicly available in a U.S. Geological Survey (USGS) report on the Internet, and also used by the Bravo Venture Group to show the location of its properties in the Cortez Trend area.
Above: Figure 5 taken from Chapter 17 "Regional Analysis of the Distribution of Gold Deposits in Northeast Nevada using NURE Arsenic Data and Geophysical Data" from the USGS article "Contributions to the Gold Metallogeny of Northern Nevada Open-File Report 98-338."
The caption reads: "Map showing isostatic residual gravity of the pre-Cenozoic [greater than 65 million years ago] basement rocks of northern Nevada (after Saltus and Jachens, 1995), gold, mercury and antimony deposits, as well as contours and axes of arsenic anomalies from soil and stream sediment samples. [Arsenic and mercury tend to precipitate out of gold-bearing fluids under similar conditions as gold and hence are viewed as tell-tale indicators]. Warm colors mark areas with rock in the middle and upper crust that are denser than those in areas marked by cool colors." The sites marked with white stars as "Granite," "SF," "Gabel," "PH," "3Bar," "NoLM," "So GB," and "So LM" are properties of the Bravo Venture Group.
According to Mr. Rasmussen, the highs portrayed in reddish colors on the gravity map to the east are on an old continental plain that contain a limestone section. The lows portrayed in bluish color to the west define the old continental slope that formed siliceous sediments. This was part of a gently sloping shelf that formed shallow sediments. The light blue area running diagonally between the two areas gives a rough sense of the old continental shelf and the Cortez Fault system that exists today. The exception is the area north of Pipeline, where White Knight things the Cortez Fault system runs vertically just west of the vertical axis of arsenic anomalies line.
Please recollect from my discussion of tectonic plate movements in Part Two that "fifty different exotic terrains were sutured on to the west coast during the Mesozoic era (248 to 71 million years ago), adding 25% to the continental crust of western North America." White Knight is looking for a gold fluid-leaking suture line where perhaps a new continental mass got slam-packed against western North America relatively early in the compression cycle.
According to John Leask, Chairman of White Knight, as one moves from west to east, there could be a 7 km difference in the thickness of the earth's crust across the Cortez Fault system related to its ancient role as a continental shelf. He also pointed out that the fault system shows 170 million year old Cretaceous intrusives. The NNE trending mountains to the west of the Cortez Fault system intersect the Cortez fault system near intrusive structures, such as a Granite Mountain Intrusive near Slaven Canyon, a Gold Acres Intrusive by the Pipeline Complex, a Cortez Intrusive by Cortez Hills, a Keystone Intrusive by Pat Canyon, and another intrusive by Celt-Teck JV on the map. (Please note that further down in this article I reproduce an aerial magnetic map created by X-Cal that shows the Gold Acres and Cortez Hills intrusives).
As previously mentioned, intrusives correlate with gold deposits along the Carlin Trend. They reflect rising magma bodies that penetrated towards the earth's surface and solidified below the surface. They help to establish the age of geologic stress events that can coincide with volcanic "reactivation" of ancient fault systems. They may also provide heat pumps that help to circulate water that in turn help to precipitate gold out of gold-bearing fluids. In fact, to this day drill holes in the Cortez Joint Venture area and in many other places throughout the Cortez Trend area show hot water.
It is important to note that the gravity map above has been calibrated to try to find certain features. At the end of this article I briefly discuss the geophysical process used to try to determine what lies underneath the surface without taking drill samples. Part of the calibration process requires filtering out certain "noise" factors. For example the Northern Nevada Rift episode that took place approximately 16 million years ago spewed out a lot of volcanic material containing magnetite. Since the Northern Nevada Rift era accompanied the gold samples found by Klondex, this magnetite is exactly what Klondex wants to pick up in its magnetic map depicted below in the Northern Nevada Rift section. However, this is also exactly what the aforementioned USGS survey and White Knight want to filter out in looking for fault structures older than 70 million years. Later in the "WNW School" section I show a gravity map created by X-Cal to show a WNW structure that does not show up on the USGS gravity map. It has apparently been calibrated differently.
Hence, these gravity studies might be both a blessing and a curse. On the one hand geophysicists can calibrate the maps to help show them what they need to know. On the other hand, they might calibrate the data gathering process to tell themselves what they want to hear based on preconceived notions, but what may not in fact lead to a realistic interpretation. Therein lies a possible danger.
CROSS FAULT VS. CORTEZ FAULT-CENTRIC THEORISTS
As previously observed, most Carlin deposits occur near a cross fault by a major fault. Perhaps the simplest explanation for this is the fact that as gold bearing fluids rise, they seek the path of least resistance. They may start in a vertical fault plane running north and south, and then seep into a fault plane running east and west, and then finally seep into and settle in a horizontal strata near the surface.
The intersections of fault lines leading into and out of the Cortez Trend area remind me of skewed asterisk (*) symbols, in which fault lines leading out of these "asterisks" in all directions are staggered up and down the Battle Mountain-Eureka Trend. .
The "vertical" of our "asterisk" consists of the the Cortez Fault system (NNW or about North 35 degrees west). This may have originated with tectonic plate rifting events that took place perhaps 700 million years ago, and may consist of very deep and sometimes parallel or juxtaposed continental shelf and tectonic plate edges that have moved against each other and have reactivated repeatedly over time. The Northern Nevada Rift may have involved a relatively recent 16 million year old reactivation through a paralleling structure. It runs about North 15-20%, or ten degrees east off the surmised Cortez Fault system.
The down-sloping rightward diagonal of our "asterisk" consists of very ancient WNW faults, that might be related to cracking along the line of thrust during the approximately 350 million year long compression cycle
The upward sloping diagonal NE faults of our "asterisk" parallel the mountain ranges and valleys that are topographically visible today. They seem to correspond to the period of extension that commenced about 30-40 million years ago.
The Northern Nevada Rift
I will start with this because all geologist agree that the Northern
Nevada Rift is very real and it has created real gold deposits. (Getting
all geologists to agree on something can be an unusual event). According
to Richard Kern, chief geologist for Klondex, the Northern Nevada rift
was created by volcanic upheaval roughly 16 million years old. It's
location is unmistakable from magnetic studies which pick up magnetite
in the basalt that flowed from it's eruptions. It is probably a geologically
recent reactivation of a much older plate tectonic fault system that
characterizes the Cortez Trend Fault system.
Source: American Bonanza
Source: Placer Dome presentations
Source: Jan 2005 Placer Dome Cordilleran Round up Presentation
Placer Dome's bullet point "NW Regional Alignment of Gold Mineralized Districts" refers to the larger white diagonal streaked parallel lines that define the Battle Mountain -Eureka Mineral Belt. The dotted white parallel lines that tilt further to the west define the "WNW Intrusive Axis Domain" structures, and are the same in concept as the diagonal parallel lines in the first slide that show Cortez Joint Venture area properties. Last, but not least, the more vertical red lines described as "NNW Structural Fabric Controls Gold Deposits" include the Carlin Fault system, the Cortez Trend Fault system, and probably the more recent Northern Nevada Rift (which may have been a reactivation of an ancient fault system). Significantly, this slide shows many parallel red lines in the Cortez Trend area, suggesting that the Cortez Fault system may have many additional faults running parallel to the east and west of it. This could make exploration really interesting in the years ahead.
Incidentally, what is excluded from the slide above are NE rifts. Please remember from my discussion of Nevada Geology 101 in Part Two that faults also tend to parallel the visible mountain ranges and valleys in Nevada today. You can get a sense of the NE direction of the terrain features from the alternating blue and purple colors in the slide above. More on NE structures later.
Source: Miranda Gold Corp.
A Gold Bar Trend running in parallel with a WNW Cortez Joint Venture Trend? Even though it seems likely that rifts paralleling the Cortez Fault system (if not the system itself) run south though American Bonanza's Gold Bar Mine, an important reason why Newmont Mining, Miranda, Bravo Venture, and Tone Resources (Nevada Gold Ventures) have staked so much property to the east is that they believe that there could be WNW-ESE cross faults that run through their properties. On top of this there could be an overlay of the Northern Nevada Rift, plus there are interesting geochemical shows in the soil and some historical mines in these areas. Lastly, there are concentrations of sedimentary rock on the east side of what could have been an ancient continental shelf.
Joe Hebert, VP of exploration at Miranda, pointed out to me that WNW theory is what helped him find the ET Blue discovery in the Cortez Joint Venture area. He was also part of the team that made the Cortez Hills discovery. It may be true that gold-bearing fluids originate very deep in the earth through a NNW Cortez Fault system, but as these fluids get closer to the surface, they seem to deposit themselves in parallel WNW "stair case" formation patterns at an oblique angle to the Cortez Fault system up the Battle Mountain - Eureka Trend.
Mr. Hebert also pointed out that lamprophyres are deeply rooted in the crust. Every one of them in the area has a WNW trend. (Lamprophyres, according to Wikipedia, are "rocks containing phenocrysts...essentially dike rocks, occurring as dikes and thin sills, and are also found as marginal faces of plutonic intrusions.) According to Mr. Hebert, lamprophyres may indicate "controlling structures" that once trapped methane gas. Then came the gold bearing fluids during the great 38 million year old event that created virtually all the Carlin formations. These fluids may have also become trapped by the same structures that had trapped the methane gas. The chemical reaction between gold-bearing fluids and the methane may have triggered "catastrophic dumping" resulting in carbon, water, and separated-out gold deposits that have "carbon front" characteristics. The methane gas subsequently got chemically converted or "cooked off."
|USGS Regional Bouguer Gravity map. Source: X-Cal. The caption has the following bullet points: "Major NW Structure, Alignment of Deposits, Periodicity of Deposits, and Major Deposits at Structural Intersections."
|USGS Regional Airborne Magnetic Survey. Source: X-Cal. The caption has the following bullet points: : "Alignment of Intrusions, Deposits Near Intrusions."
Source: CMQ Resources
Source: White Knight Resources
Source: White Knight Resources
. Source: White Knight Resources
Source: White Knight Resources
Flag carried by the 3rd Maryland Regiment at the Battle of Cowpens, S. Carolina, 1781
William Fox. Sometimes
William Fox offers viewpoints that are not necessarily his own to
provide additional perspectives.