{"id":128,"date":"2018-03-24T11:59:34","date_gmt":"2018-03-24T18:59:34","guid":{"rendered":"http:\/\/mollymarieprospect.com\/blog\/?page_id=128"},"modified":"2022-10-17T17:45:42","modified_gmt":"2022-10-18T00:45:42","slug":"ore-genesis","status":"publish","type":"page","link":"https:\/\/mollymarieprospect.com\/blog\/geology\/ore-genesis","title":{"rendered":"Ore Genesis"},"content":{"rendered":"

The Molly Marie IOCG deposit was formed when much of what is now southern Arizona was covered in deep brine lakes (see Setttings page).\u00a0 The largest producing gold mine in Arizona (500,000 oz.) was the Copperstone Mine, located north of Quartzite, AZ, and it was an IOCG deposit also, formed in the Mid-Tertiary.<\/p>\n

The Molly Marie is the Magmatic-hydrothermal type of IOCG shown on the left side of the diagram below (the missing piece is the brine lake which will be shown below).<\/p>\n

The diagram below is from the paper “Magnetic Survey for Iron-Oxide-Copper-Gold (IOCG) and Alkali Calcic Alteration Signatures in Gadarwara, M.P, India: Implications on Copper Metallogeny” by P.V. Sunder Raju<\/span> and<\/span> K. Satish Kumar<\/span><\/p>\n

The following link is to the paper:<\/p>\n

https:\/\/www.mdpi.com\/2075-163X\/10\/8\/671\/htm<\/a><\/p>\n

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Magmatic hydrothermal IOCG deposit (left side)<\/figcaption><\/figure>\n

The brine lake that accompanies this deposit is not shown, but is shown in the diagram below.<\/p>\n

The Molly Marie ore was derived in a similar fashion as the left side of the diagram and was facilitated by surface brines that were circulated from extensive brine lakes.<\/p>\n

Below is a diagram of the Molly Marie Prospect Ore Genesis Model created by the author (years ago before the above diagram was seen).\u00a0 What is believed to make the Molly Marie Prospect much richer than even a typical gold rich IOCG deposit is the great amount of metal rich volcanic debris (from the carapace of a porphyry) that was available to be leached by the brine (see photo of porphyry below).\u00a0 As plainly evidenced by the remnants of the volcano’s slope on the east side of the caldera and the height of Superstition Mountain, the volcanic debris could have been as deep as 3000′ near the vent and in the area.<\/p>\n

\"https:\/\/mollymarieprospect.com\/IOCG\/modelx.png\"
The Molly Marie Prospect Ore Genesis Model.<\/figcaption><\/figure>\n

An important feature that is also present where the ore fluids “leaked” though the basalt and deposited on top on the Molly Marie Prospect beneath the brine lake are hydrothermal mounds as shown in the diagram below.\u00a0 As shown on the Introduction page, there are several fully intact large mounds in Area 3 (Areas are described below).\u00a0 The mounds shown below are what is typical for a VMS deposit; the mounds on the prospect are similar, but with much more magnetite.\u00a0 As stated on the introduction page, there is now evidence from deep sea mounds that there can be 5x the volume of the mound in ore below the seafloor.<\/p>\n

What has even greater potential and is shown in the diagram above, is the possibility of a very large orebody in the arkose breccias and beneath the basalt.\u00a0 a large amount of saccharoidal silica has been found on the breccias which were once hydrothermal vents.\u00a0 Some fossilized microbial mat was found with barnacles also.<\/p>\n

\"https:\/\/mollymarieprospect.com\/update\/mound.jpg\"
Hydrothermal Mound Genesis<\/figcaption><\/figure>\n

Below is a link to an excellent paper regarding IOCG deposits in North and South America.<\/p>\n

https:\/\/www.geo.arizona.edu\/~mdbarton\/MDB_papers_pdf\/Barton09_CordilleranIOCG_SGA.pdf<\/a><\/p>\n

Below is another in greater detail from the University of Arizona regarding\u00a0 IOCG deposits.<\/p>\n

https:\/\/www.geo.arizona.edu\/~mdbarton\/MDB_papers_pdf\/Barton[14_IOCGSystems_ToG2-Ch20.pdf<\/a><\/p>\n

The nearby Goldfield mining district, approximately 2-1\/2 miles away, was the result of the same basic ore-forming processes that took place at the Molly Marie.\u00a0 The Goldfield district is also located on a submarine collapse caldera located above a magma chamber.\u00a0 In the Goldfield district there were many small mines on the caldera margin, and two of them\u00a0 (Mammoth, Old Wasp) were very notable for not only their documented bonanza gold grades, but because of their written description and the visual below, where they appear to have been unrecognized as the upper extensions of an IOCG deposit.\u00a0 As shown in the photo below, all mines were located on the periphery of the caldera in or near iron oxide-altered breccias.<\/p>\n

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Goldfield Caldera and key Mines<\/figcaption><\/figure>\n

The Mammoth Mine was over 1000 feet in depth.<\/p>\n

In the booklet, “Goldfield Mining District Geology and Ore Deposits”, John Wilburn describes the mines there and some of the ore.\u00a0 The Mammoth, was the highest producing mine, largely due to the “Mormon Stope” that was found in 1892\u00a0 after it was struck 35 feet below “Weekes Wash”.\u00a0 This was supergene gold ore that ran hundreds of ounces to the ton.\u00a0 The Mammoth reported\u00a0 production of over 50,000 ounces of gold, but considering the bonanza high grade and the great amount of theft that was documented at that time, the production could have easily been more than double that.<\/p>\n

Excerpts from Mr. Wilburn’s description of the Mormon Stope:<\/p>\n

“This ore body was located at the intersection of a cross fault within a high-angle sheeted or shear zone in arkose dipping west 83 degrees, 30 feet wide, and 200 feet in length.” and, “The ore body extended from near the surface to the 200 foot level carrying hundreds of ounces of gold per ton. Considerable electrum occurred abundantly free as wire, dust and flakes in white to glassy crystalline quartz stained extensively by pyrolusite, hematite, and limonite derived from oxidized pyrites.\u00a0 No electrum occurred in the dacite dike; brecciated arkose on the contact hosted some of the richest ore”<\/p>\n

Wilburn’s description of the Old Wasp ore (found in 1983 with a backhoe) is as follows:<\/p>\n

“The ore shoot was 8 feet wide and 50 feet in length.\u00a0 On the east footwall, free gold occurred with galena, anglesite, malachite, chrysocolla, and hematite in an extremely heavy ore 12 inches wide that assayed 244 opt gold and 56 opt silver. \u00a0 The sulfide ore was of limited size.\u00a0 At 35 feet in depth the ore values diminished. An old drift underground struck the ore shoot on the 1,022 foot level where gold values averaged 0.66 opt along 40 feet of drift. ” Author’s note: the 1022 foot level was that of the nearby Mammoth Mine. Wilburn also describes all of the ore in Goldfield as being heavy with “drusy quartz”. Drusy quartz are crystals that cannot be seen with the naked eye.\u00a0 Drusy quartz abounds in the breccias at the Molly Marie Prospect.<\/p>\n

The author spoke with Mr. Wilburn about the Mammoth and The Old Wasp Mine.\u00a0 He said he had held some of the Old Wasp ore in his hands, and he stated that the Mammoth ore had significant galena also.<\/p>\n

Wilburn stated that at the lower depths of the Mammoth considerable chalcopyrite was encountered.<\/p>\n

Here are some more excerpts for other mines from “Goldfield Mining District, Geology and Ore Deposits” that indicate an IOCG deposit:<\/p>\n