Rich Hill Geology

[Dutchman]

I have been hunting Rich Hill for some time now, and have always wondered how the Gold got to the top of Rich Hill. I have found my fair share of nuggets off the slides which are mostly well worn and smooth. I can only assume that the area had a lot of water at one time. Assuming that the gold was deposited from water action one must ask himself, “From what direction did the water run, North, South, East or West? Where did the gold originate before it was moved? I know some of you have your own ideas and I would like to hear them. No idea is too silly to discuss, that’s how we all learn. I especially would like to hear some of the home brewed ideas, a lot of us have heard most of the scientific theories already, but these theories always leave me hanging at some point. Lets have a friendly discussion about each others thoughts. So who wants to go first?

[DOC]

Chris Gholson collaborated on a book all about Rich Hill. The book was amazingly detailed and covered geology and just a lot of little known facts.

I am sure Chris may have some of the books still available.

Doc

[Dutchman]

Chris Gholson collaborated on a book all about Rich Hill. The book was amazingly detailed and covered geology and just a lot of little known facts.

I am sure Chris may have some of the books still available.

Doc

Thanks Doc,

I have read Chris's book. It was a good read, but falls short of an explanation of how the gold was deposited where it is found today.

[Dakota Slim]

Earl, I'm not so sure the smoothness was caused by water. Many of these nuggets are heavy slugs which show little or no evidence of pounding by rocks as you would expect to find in a riverbed. It could be that heat made them into the fat little blobs that they are.

Whatever forces it took to create and manipulate them into what they are will probably never be know with any certainty. I've seen Australian nuggets which appear to be similar.

I'd like to hear what Chris Gholson has to say.

[nuggethunting]

Hello Guys,

The book you're talking about is co-authored by several people including Chris Gholson. A good friend of mine, also part in the Rich Hill book, Dr. Erik Melchiorre is currently finished the book titled "The Octave Gold Mine," which was one of the richest vein deposits in the Rich Hill area. Dr. Melchiorre has a PhD in Geology and specializes in Stable Isotope Geochemistry. I carry both of these books if anyone is interested in getting a copy. There is also something else coming out soon that I helped on, but can't really say much right now.

I've spent the last 15+ years tromping around Rich Hill, walking from one end to the other, from the bottom to the top of all the ridges. What I can tell you is there are multiple sources of the placer, but many of the old vein systems have erroded way or pinched off. The entire area was formed by uplifting and dropping, or what you can call "Basin and Range" faulting.

At Rich Hill you can find a wide variety of gold nuggets and specimens. Most of the typical gold nuggets are coarse slugs of gold, while other pieces can be attached to ironstone, country rock or quartz. Some of the gold nuggets I have found out there are very crystalline and are sharp enough to cut your finger open.

Take care,

Rob Allison

[DigDeep]

Cool rob, now you are a movie star and an author.

[vini]

Chris Ralph is another extremely knowledgeable guy I like reading his articles in ICMJ

[Bandana Don]

Rob: From all I've read about Rich Hill's geology and gold veins I believe what you posted is the best explanation.

Don

[Chris Gholson]

Hi Guys,

One of the biggest mysteries surrounding Rich Hill has always been, “How did the gold get on top of the mountain?†While doing researching for the book we heard some interesting theories. Some felt that the nuggets actually originated from the Vulture lode to the south and were transported along the bottom of an ancient river until they ran across the top of Potato Patch where they became trapped in the crevices amongst the granite boulders. Another theory was that a powerful volcanic eruption occurred in the vicinity of the Potato Patch. The molten gold was spewed into the air where it cooled and scattered itself for miles around the mountain. Although I am not a geologist, I have spent many years exploring and prospecting the area and have developed my own opinions as to how the gold got there. Even though there is basalt on the flats around Decision Corner I think the volcano theory can immediately be scratched off the list, and the Vulture-Ancient River theory, although possible, not very likely. While the Vulture lode produced some excellent placer deposits, it seems like a very big coincidence that this gold happened to be deposited on a mountain that contains lode gold deposits of its own. Not to mention many of the nuggets found here are rough & angular in appearance, and there has also been a great deal of specimen, or gold/quartz float found here as well. If this gold had been transported for many miles in an ancient river we would expect it to be smooth & sluggy, similar to that found in the Mother Lode. Usually the most simple theories are the right ones, so personally I feel the gold at Rich Hill originated locally.

At first glance the granite ‘bouldery’ terrain does not look like typical gold country, so it is easy to understand how different theories got started. However, with a closer look we find that Rich Hill does share qualities found in other famous gold producing areas around the world. Rich Hill itself is granite, but it is surrounded on the west, north, and east by schist. We also see this in the Bradshaw Mountains where the main mountain chain is granite while all the surrounding foothills are made of schist. Geologists believe that millions of years ago central Arizona lay at the bottom of an ocean. At some point plumes of magma pushed up and intruded the sediments at the bottom of this ocean. The magmas rich in quartz slowly crystallized into granite. This granite pushed upwards and ‘cooked’ the sediments and metamorphosed them into Yavapai Schist, or ‘greenstone’. It is believed that a later intrusion of hot magma occurred which formed the diabase dikes. The dikes themselves usually don’t contain gold, but they boiled the groundwater around them and created hydrothermal cells. The hot water mobilized the gold, silica and sulfides in the schists, and when they eventually cooled, gold-bearing lode veins were formed. When the Basin & Range Formation occurred Rich Hill rose high above the valley and the mountain itself was formed. This uplift, along with normal mechanical & chemical weathering began to wear down the new mountain. The gravels eroded from the mountain washed down and formed the alluvial deposits of Weaver and Antelope Creeks. The material on top of Potato Patch most likely weathered in place forming one of the richest eluvial deposits ever discovered in the state.

Obviously no one was around to witness this event, but since we find similar conditions in other gold-bearing locations around the world, this idea seems the most plausible. However it happened, one thing is certain, the mountain known as Rich Hill was filthy rich in gold! Since its original discovery in 1863, it has given up 1000’s of nuggets ranging in size from pinheads up to lumps weighing a pound or more. It is a fascinating place, rich in both minerals and colorful ‘wild west’ history. If you’ve never been, grab your metal detector and pay a visit; there could be a whopper waiting with your name on it!

P.S. I wanted to thank Doc for mentioning the book I coauthored about Rich Hill. It was an exciting project to work on that took nearly three years of research for us to complete. If anyone is interested I do have copies available, or you might be able to pick one up at Barnes & Noble.

Here is a photo of Rob & I standing on the historic Potato Patch taken in the late 1990's.

[whats4supper]

at one time, the continental subduction zone was located in Colorado, and volcanic activity, plumes of plutons (molten globs of granite/magma) rising upward, creating mineral and metal zones that are now exploited for ore. Over the passage of milenia, the subduction zone has gradually moved westward, from Colorado, to California and offshore. as the volcanic activity moved, it created igneous and metamorphic activity creating a wide range of mineralization throughout the West, along with mountainous uplift, faulting, and rift zones.

The dry land crust of the Earth is thinnest in the Great Basin, averaging 12 miles thick, as opposed to thicker parts up to 22 miles in other parts of the dry land continents.

One always has to comprehend that the mountains we see today, are not the mountains of old, which were higher or more massive. where did the old mountains go? Erosion carried those bits and pieces to fill in the valleys that we now see as Phoenix, Las Vegas, and the myriad rest of the world, and the mountains we see now, are what's left.

The gold we find, if not in a vein, were the bits and pieces exposed and eroded out of the ancient veinstocks, that sank down into whatever trap or pocket existed at the time. Paystreaks whose overburdens have also eroded and flowed down into the valleys, leaving the nuggetshooter with a metal detector a chance prime opportunity....

movement and erosion still going on: http://quake.wr.usgs.gov/recenteqs/

[Dutchman]

Good input guys Just wondering if a sample of gold from the Octave mine would be chemically consistant with a sample of gold from the top of Rich Hill and/or the Devils Nest? I happen to have multiple samples for each of these locations. I don't have any samples of gold from the Johnson mine area or the Myers mine area though. Does anyone no if a chemical analysis has been performed on these deposits?

[nuggethunting]

Hey Dutchman,

Wish I could talk more about this, but not at this time. All I can say is what you're asking about is being done right now. Many of my specimens and nuggets have been linked to various vein systems around Rich Hill. If I see you around this weekend I will explain more off the record.

Take care,

Rob Allison

[azaware]

When the Basin & Range Formation occurred Rich Hill rose high above the valley and the mountain itself was formed. This uplift, along with normal mechanical & chemical weathering began to wear down the new mountain. The gravels eroded from the mountain washed down and formed the alluvial deposits of Weaver and Antelope Creeks.

Hey Chris

I think your analogy looks pretty right on. I’m not sure if we have a different, but what do you mean about uplift? I don’t think Rich Hill itself uplifted, It may of uplifted with the hold high county to the North uplifted if that is what happened. I think Rich Hill and the land to the West North and South was all at pretty much the same ground level. And with the natural eroding formed Weaver and Antelope Creeks.

Kim

[nuggethunting]

Hello Azaware,

I would have to agree with Chris and the Geologists on this one. Most of the mountains ranges are uplifted and this would include Rich Hill itself.

Talk with you later,

Rob Allison

[montana]

I agree fully with what Rob, Chris, and Whats4supper added. What has really puzzled me is the massive alluvial fans that were deposited where Antelope and Weaver Creeks issue onto the flats carrying cars sized boulders far from the mountain. These are evident when veiwing aerial photos of the area or veiwed from high on the hillsides. With the relatively small drainages of the creeks the fans seem way out of proportion. Since moving to Yarnell which is relatively close to Rich Hill and in the same uplifted block of granites , some things have become apparent which may shed some light on this. Yarnell and the southwest side of the Weaver mountains get massive amounts of rain during the winter months many years. Two years since living here we have had nearly 40 inches of rain during the winter which is far higher than most places in Az. The explaination for that would seem to be the fact that the abrupt uplift with a southwest exposure to the pacific storms which come from the Southwest causes the phenomenum known as orographic lifting which in effect wrings the moisture from the clouds as the fronts hit the face of the mountains and rises over them. This extra dose of rainfall would help wash away the soils leaving the heavier materials like gold behind where it was trapped in the nooks and crannies atop Rich Hill. What gold that managed to escape the traps made it to the creeks and was carried far out onto these alluvial fans. This would also explain the high proportion of specimen gold found out on these fans. The lumps of quartz with gold in them would be transported almost as easily as a quartz rock without any gold because the specific gravity wouldn't be altered by much. Thanks to these alluvial fans the Rich Hill gold area isn't confined to just the mountain itself, but is scattered far and wide as far as 5 miles or more from the Hill. The heavy rains also have the effect of washing topsoil away which leaves much of the remaining gold within reach of our detectors. Jim Straight explained how this works in desert areas in the 2008 annual edition of Silver and Gold magazine. It is called soil deflation or soil depletion concentration with soil being removed either by water or wind, removing the lighter topsoil and exposing the once buried gold. The forces of Mother nature have come together at Rich Hill to give us a huge place to play with our detectors and dry washers where the gold is within reach of simple hand tools and is found by kids ,elderly retirees, and everyone in between. Every year fantastic finds still come to light there despite over 150 years of diligent activity. The various prospecting clubs make it possible for everyone to have a chance at finding some Rich Hill gold and most are succesful if they put in a little time.----Bob

[claim jumper]

http://maps.google.com/?ie=UTF8&ll=34....mp;t=h&z=12

[whats4supper]

basically, granite is molten continental rock that happens to be less gaseous than explosive magmas. but is magma nonetheless. However the granite is a magma that cooled off before erupting or venting through a volcano. with that in mind, no matter what uplift occured to form the mountain, there was still some sort of encasement above the granite (pluton) that allowed it to cool, instead of forming a volcano.

In a subduction zone, the heat of the faults and upper mantle dissolves most any kind of rock traps in that furnace. however, the molten stuff is lighter than the surrounding rock, and it starts to rise by nature, both dissolving/melting country rock above, as well as heating adjacent rock mass (metamorphism); much like the blobs in a lava lamp. Much of the igneous rock is chloritic, allowing the vaporous transport of gold and other metals. Chlorine is a principal base component of cyanide treatment to retrieve gold from ore. not many things affect metallic gold, but chlorine is one that does, and in a big way. as rising vapors cool, metals drop out of solution into cracks and voids.

Many geologists believe that gold comes up as a vapor in concentration during an eruption, or fumarole out of super heated vents in a volcanic field, and can be a very rich surface phenomena and deposit. certainly Goldfield, Quo Vadis (S of Henderson, NV) and portions of the Bradshaws, among others, reflect these views. Of note are that other minerals are transported in much the same way, such as silver, chromium, platinum, cobalt, copper, etc. Many such deposits are relatively shallow, and once worked out, don't seem to extend very deep. Gold ore from the Quo Vadis had a relative worth of $80,000 to $120,000 per ton, at $20/ounce gold. I am sure that the gold of the Octave Mine, Rich Hill, La Paz Placers, are of a similar origin.

[Tony Teixeira]

Chris Ralph is another extremely knowledgeable guy I like reading his articles in ICMJ

Not only that he has an awesome website with tons of information, I have spent hours surfing his site..... here is one of my favorite starting points, http://nevada-outback-gems.com/prospecting...tect_possib.htm

Vini, I am sure you have already been through Chris's site a few times but for those who have not..... Check it out!

Tony Teixeira

[Reno Chris]

Thanks, Tony!

Chris Gholson's descriptions is a pretty good summary of Rich Hill, but with a few alterations could describe a lot of gold deposits.

Nearly all gold deposits are the result of circulating hot geothermal waters. The temperatures vary somewhat, but all are far below the temeratures needed to melt gold. Gold is not carried in a vapor phase, its a liquid phase. After much study, geologists have concluded that sulfur in an acidic form (bisulfide) is the chemical that carries the gold in silution in nearly all cases. At high tempertures and pressures Hydrogen sulfide (H2S) disolves metallic gold into liquid solution. Circulating waters (heat rises) carries the disolved gold upward toward the surface where the solutions cool and drop their gold. Other things besides cooling can also make the waters drop their gold as well. Now all this stuff happens from a thound feet to several miles below the surface. Uplift has to bring it up to the point where we can see and mine it.

Goldfield and Quo Vadis are both examples of near surface epithermal gold-alunite deposits and have some definite things in common geologically - both produced some incredibly high grade ores. The Bradshaws and Rich Hill are deeper mesothermal low sulfide quartz-gold deposits and their geolgy is more closely related to the mother lode deposits in California.

Free chlorine and cyanide in the presence of oxygen both dissolve gold, but they are completly different and there is no chlorine in cyanide (the cyanide ion is made of carbon and nitrogen).

The types of magma that can cool to form granite can have loads of gasseous material in them - they are often responsible for great volcanic explosions. Mt St. Helens had a bunch of rhyolitic / granitic type magama in it, and BOOM - those gasses in the magma were what caused that mountain to blow up into a pretty spectacular explosion. Cauldera volcanos also have high silica tyes of magma that are of the rhyolitic / granitic types and they cause explosions that make Mt St. Helens look like a toy pop gun by comparison.

This month's ICMJ features an article on "Reading a river for paystreaks"

Chris

[whats4supper]

thanks Reno Chris! there are always two sides to any story, sometimes more.

[montana]

Reno Chris. I've often noticed that what is commonly called granite at Rich Hill is actually quite different from granites in other places and although it probably could be called a granitic type of rock, is it really a true granite? In places it looks like something of a blend of granite and rhyolite. What exactly would it be called technicly speaking?----Bob

[Reno Chris]

Hi Bob -

You have spent an awful lot of time up on those hills around the Rich Hill area and you really know the area like the back of your hand. For me, I have really spent only a little time actually prospecting there - I have only been there during Chris G's outing, and usually I am gabbing with other prospectors. I have seen some dikes and other intrusive rocks like diabase up there. What I have seen of the granite there is pretty standard stuff, but I wouldnt doubt that there is some more unusual looking material up there that I just have not seen.

Perhaps we can talk more about it in February when we are up there.

Chris

[mbcougartl]

Hey azaware and Reno Chris...I inform you that Rich Hill is a prehistoric extinct volcano. I went there few times to see alot of rich mineral especially gold, pyrite, any sulfide minerals, quartz and gemstones. Reno Chris explained this to me very clearly. Yes, I am interested to read the book "Rich Hill" authored by Chris Gholson. I would like to buy it soon. Excellent job Reno Chris to help us to understand the detail of Rich Hill.

[montana]

Reno Chris. When you come down we'll go for a little ride. I'll show you what I'm talking about. I can also show you where I dug out a 10 ounce in situ pocket in schist with no quartz. You might find it interesting and fits right in with the long thread on AZO a while back. See you in Feb.---Bob

[Dutchman]

I have heard from several people that think that there is/was a steam vent or gieser at the top of Rich Hill. Does anyone else have any information about this?