The Cortez Story - Part Five: Cortez Trend Maps, Pictoral Overview (2)
Precious Metals Special Report
... Part One: Overview
... Part Two: The Fundamentals
... Part Three: Overview of Players, Two Majors
... Part Four: Profiles of Sample Junior Players
... Part Five: Cortez Trend Maps, Pictorial Overview
Part Five: Cortez Trend Maps and Pictoral Overview (2)
The Northeast School
Please recollect from Geology of Nevada paper cited in Part Two that faults tend to run on each side of mountain ranges. The mountain ranges and valleys visible today tend to trend NNE on the west side of the Cortez Fault System, and more NE on the east side.
I think that the most plausible cause of the NE direction of the mountain trends is the fact that they probably lie perpendicular to the direction of the compression force vectors that occurred for several hundred million years. Compression can create perpendicular mountain range folding, uplift, and overthrust faulting. According to one source, "The Rocky Mountains in the west-central United States are an example of folded mountains produced by compression along an oceanic/continental plate boundary." The Farallon plate "dragged along the bottom of the continental crust of the North American plate, causing significant folding, and faulting of rocks, especially in Utah and Colorado." These compression force vectors could slide at an oblique angle over more ancient structures such as the NNW Cortez Trend Fault system.
During the continental stretch cycle that began 30-40 million years ago, "fault-block" mountain ranges in the Basin and Range area have apparently developed parallel to structures created during the compression cycle. Geologists have observed parallelism between compression structures and the structures that form in a later extension cycle. This could be an indirect and perpendicular way that the WNW and NE schools are related to each other.
A geologist told me that compression usually does a poor job of creating vertical fault structures compared to extension activity. If this is true, the vertical NE structures that exist today likely came about in the extension era following the main 38 million year old Carlin gold deposit event. This means that these structures are hence unlikely to hold Carlin-style gold deposits because they came after the main event that created most of these deposits. However, NE structures could still hold some gold from more recent volcanic activity, such as what happened during the sixteen million year old Northern Nevada Rift era.
Please note that earlier in this article I provided two illustrations of J-Pacific Gold's Golden Trend property from David Shaddrick's geological report that show examples of NE structures.
White Knight's proprietary gravity map shows an interesting NE-trending cross fault labeled "Tonkin Summit Fault Zone." The northern edge of the fault zone runs through the southern part of BacTech's property. Starting from the southwest, its northern edge runs through Nevada Pacific (JVed with Placer Dome), BacTech, and White Knight's Indian Ranch (JVed with Placer Dome) properties. Its southern edge runs through White Knight, Miranda, Bravo Venture, and Minterra properties. John Leask also pointed out to me that it is quite interesting that the mountain ranges, which are paralleled by faults, tend to intersect the Cortez Fault system at intrusives.
Source: CMQ Resources
Also, CMQ Resources provides a map (right) that shows the NE trending Crescent fault that runs along the southern edge of the NE trending Crescent Valley. According to Martin Lambert, the CEO of CMQ Resources, a head geologist at Goldfields (which acquired 10% of his company) has been closely analyzing data in this area. Various people who live in Crescent Valley, NV have hot springs literally in their back yards. Please also note on the Intierra Mineral Information map at the beginning of this article that the Cortez Joint Venture has a huge land track next to his, so maybe the folks at Placer Dome and Kennecott see something as well.
A Tale of Two Anomalies
CMQ Resources mentions two major anomalies at its web site. The first anomaly is the possibility that there might be a horst block formation right in the middle of alluvium-filled Crescent Valley that CMQ Resources has found at roughly a 1,500 foot depth. CMQ calls this the "Montezuma Horst." The second anomaly is CMQ Resources' observation that the Pipeline Complex's gold deposit seems to be relatively flat and not deeply "rooted," unlike the Cortez Hills discovery where Placer Dome has drilled down to 2,500 feet and has not found a bottom to the deposit yet.
One theory is that the Cortez Fault system is not a key player in the creation of the Montezuma Horst, but rather it reflects a splay off the ENE-trending Indian Creek and Thomas Creek faults shown on the map. An alternative theory could be that a magma vent ran from very deep in the Cortez Fault system diagonally out into Crescent Valley to create an intrusion. A third possibility could be that another very ancient NNW fault system runs parallel to the Cortez Fault system near the presumed horst structure, similar to the parallel red vertical lines on the Placer Dome map I depict earlier in this article.
The CMQ Resources map above has turquoise arrows illustrating a theory that the Pipeline deposit may have originally formed near the alleged Montezuma Horst and then somehow drifted SW down Crescent Valley towards its present location. This last theory is an "outlier" since it does not mesh well with the Compression-Extension cycle theory that I have already discussed. In fact, CMQ's CEO, Martin Lambert, told me that he wanted to make it clear that this is only one of many hypotheses that his company is currently investigating, and it is by no means a proven theory. According to David Shaddrick, the aforementioned geologist who works with J-Pacific Gold (who also wrote a technical report for CMQ Resources), a hole drilled by CMQ Resources found an intrusive, but beyond that, such as whether this structure can be called a horst, is still not known for sure.
Source: CMQ Resources
The debate over a "host rock" versus a "structural" formation
The geological anomaly we are trying to explain is why the Pipeline complex is a horizontal "host rock" deposit that seems to lack strong "roots," whereas the Cortez Hills deposit is a high angle "structure" play with apparently deep roots. Can they both be related to an underlying Cortez Fault system?.
This diagram above shows how the Pipeline deposit is hosted within Lower Plate Rocks. At one time the upper plate rock may have helped to trap the gold bearing fluids and caused them to pancake out. Erosion of the upper plate stratum in recent geological history has made the gold deposit more accessible for open pit mining.
Incidentally, to the left in the chart above we see a very old Quartz Monzonite intrusive (the label "Cretaceous" suggests an age of 71 to 144 million years). It is designated as the Gold Acres Intrusive in the aforementioned X-Cal magnetic survey map. It is interesting how the lower plate strata holding the Pipeline Complex looks like it has been pushed up to a higher level by the presence of the intrusive. We need to remember that everything is relative in Nevada geology, and this could be due either to a volcanic uplift, or else related to a drop in relative elevation of both upper and lower plate strata along mountain slopes during the extension period that began 30-40 million years ago. Or it could involve some combination of the two.
The diagram shows a "skarn," which consists of "lime-bearing silicates, of any geological age, derived from nearly pure limestone and dolomite with the introduction of large amounts of Si, Al, Fe and Mg and usually formed near an intrusive contact." As mentioned previously, the existence of an intrusive can suggest a very deep fault structure, which is good indicator of a possible deep source of gold-bearing fluids, and can also indicate the presence of a heat source that can help circulate water that can in turn help precipitate gold.
Joe Kizis, President of Bravo Venture Group, explained to me how the Pipeline and Cortez Hills deposits could have very different shapes and orientations, and yet still ultimately be "genetically" related to the same underlying Cortez Fault system.
In a host rock play, gold bearing fluids may have seeped into the deposit area from any number of cracks below without precipitating out of the lower rock. Then the gold-bearing fluids may have hit a cap rock that caused them to pan cake out in a horizontal host rock stratum. This could give the appearance of being shallow and "rootless."
The host rock stratum itself may have been formed through a process called "duplexing." This can occur when one strata thrusts and then curls over the other, spiraling like the dough in a jelly roll. The friction between the strata may have created beds of rock fragments (brecciation) that can be ideal for hosting a deposit.
I might add that John Leask of White Knight offered me the opinion that the Pipeline Fault is part of the Cortez Fault system, and runs along a same NNW trend. Dr. Ken Snyder was fairly certain the Cortez Fault system ran through the area. David Shaddrick of J-Pacific Gold thinks the Pipeline Fault might be the Cortez Fault. Given the old saw that geologists rarely agree on anything, perhaps this a good start on a "genetic" connection consensus.
Meanwhile, over in the Cortez Hills discovery area, the gold bearing fluids moved into a high angle fault structure that may have been filled with brecciated rock or some other hosting material. The upward rising gold-bearing fluids apparently ran into something like methane gas, ground water, iron in the rocks, or something else, or some combination of all of the aforementioned, that caused the gold to rapidly precipitate out of the gold-bearing fluids and create a deposit. It probably has a "genetic" connection to a deeper Cortez Fault system as well.
The Cortez Hills deposit is a "high angle" structure only 400 feet wide in places, that starts 400 to 500 feet below the surface, and drops down 2,500 feet with no bottom found yet.
Placer Dome spent 2.5 years drilling in the Cortez Hills area before the company found the deposit. Most Carlin structures are similarly "high angle." Obviously a lot of deep saturation drilling will be required to find more of these kinds of structures in the future.
Other Tools of the Trade
Perhaps most readers are familiar with how the development of 3-D seismology in the oil and gas business has increased "hit" rates from perhaps about one in twenty several decades ago to as high as 50% in certain areas. White Knight geophysicist Hans Rasmussen gave a presentation on Dec 10, 2004 before the NW Mining Association regarding how conceptually similar techniques are making headway in the mining industry to improve the odds in developing drill targets. He was kind enough to allow me to reproduce some pictures from his presentation. The new odds are certainly not 50%, but they might very well now be somewhere above the 1-2.5% bracket for drilling prospects depicted in John Kaiser's chart in Part Two.
Source: White Knight Resources
The diagram in the upper left in the chart above shows a model of a horst block formation. The chart also explains abbreviations for different types of rock that tend to both comprise and surround horst blocks in northern Nevada. Horst blocks are made of Lower Plate sedimentary rock which have optimal characteristics for hosting Carlin-style gold deposits.
Each type of rock has different characteristics in terms of its density, magnetic susceptibility, and resistivity. Explorers can shoot sound waves down into various strata and get various density readings from computerized analyses of echo effects. They can also mount devices on airplanes and ground vehicles to provide magnetic and resistivity read-outs as they systematically canvass areas of interest.
Source: White Knight Resources
From "reality" to building a sensor readings database. The geophysical modeling process starts by calibrating the read-outs of these different sensors with known geological features. This is the geophysical forward modeling phase. Each set of magnetic, gravity, and resistivity readings is associated with particular geological features and then filed away in massive data banks. After the computer is fed a vast data base of real world associations, it is now ready to work the process in reverse with geophysical inverse modeling.
Source: White Knight Resources
Using the sensor readings database to reconstruct a likely reality. Here we start with the sensor data, and then ask the computer to show us what underground structures might have the best correlation with the information. In the picture above, the geophysical inverse modeling example shows us where a possible lower plate formation may come closest to the surface. This might offer us a prime drilling target.
Source: White Knight Resources
The illustration above shows how White Knight has used inverse modeling to try to identify a possible horst block target on its McClusky Pass property.
Of course what the White Knight folks really want to see is geophysical evidence that they are right on top of a major Cortez Trend fault that penetrates very deep into the earth's crust. It would also help if it is bordered by horst blocks that show parallel "controlling structures," if it hosts major Cretaceous and other ancient intrusives, intersects WNW and NE and NNW cross-faults, shows ample evidence of numerous re-faulting and volcanic "reactivations," is rich in brecciated Lower Plate silty quartz component siltstones host rock, has evidence of extensive hydrothermal activity, and is loaded with mercury, arsenic, antimony, and other "pathfinder" surface anomalies.
All of this, plus drilling results that hopefully show bonanza grade gold deposits, and the Holy Grail at last!