The Molly Marie Prospect is a group of 20 contiguous mining claims located in Maricopa County, Arizona.  This website describes the exceptional geologic features of the Prospect that includes a very large, fully intact, IOCG (Iron Oxide Copper Gold) ore deposit located in a previously unrecognized submarine caldera over one mile in diameter.

Below is a photo showing the extents of the massive iron-oxide altered breccias of the deposit before they dive under basalt and silica mounds to the east.  The abundant hematite breccias on the hill or bulge in the basalt labeled “Cerro Negra” are not indicated, but are described within.  Please note the highway located approximately 600 yards to the west of the caldera.  The igneous rock exposed at the neck is  an oxidized magnetic, brick-red, Rhyolite porphyry.
The Molly Marie Collapse Caldera

Accompanying this deposit, located near the foot of the Superstition Mountains, is a subject that must be breached:

A “missing” mining district, The Peralta Mines.

The location of these legendary mines has commonly been thought to be deep inside the Superstition Wilderness area, but it’s just outside its boundaries.  All of the stories told about lost mines in the Superstitions during the past 125 years have one thing in common; they do not have any geology to back them up, on  a district scale.  The geology of the District shown within proves the existence of the IOCG deposit, and proof that the District was mined by the Spanish and Mexicans (also shown within),  demonstrates that the IOCG deposit is the most sought-after kind………. an exceptionally  gold-rich one.

Proof that the Spanish and Mexicans mined the District also helps explain why a deposit so immense could go undiscovered; all of the most obvious outcrops indicating ore were simply removed and the pits (and shafts) were filled back in;  intense alteration zones still betray their locations.

The root-cause of the richness of the deposit is likely the rock exposed at the volcanic neck: a  pre-enriched porphyry.  The below photo shows what a portion of the volcanic neck looks like.  The color of the porphyry betrays its high iron content.

Rhyolite Porphyry of the Molly Marie caldera

Dikes of magnetite rich rock on the prospect indicate the source of the iron for the IOCG deposit.  After the Molly Marie volcano’s last eruption, the iron rich rock at the bottom of the magma chamber remained, and magmatic fluids ascending from there reacted with metal-rich brine descending from a brine lake above, creating the IOCG deposit.  The lithology above the magma chamber rested upon the remaining iron rich magma and became highly magnetized and iron altered.

Magnetite-rich rock from bottom of Magma Chamber

The nearby Goldfield mining District, 2-1/2 miles away, has geologic features similar to that  of the Molly Marie Prospect, including a caldera with breccias on its margin.  Significant gold ore was mined there, in breccias, that assayed hundreds of ounces of gold to the ton;  the volume of breccias at the Molly Marie caldera is multitudes greater than those at Goldfield.

The rarity of this type of IOCG deposit, the magmatic hydrothermal type (MH-IOCG), almost completely intact and exposed at the surface as shown below, cannot be overstated.

Below is a hand sample of rock from the Molly Marie that is exposed in a wide zone approximately 400 yards long in the arkose breccias that is aligned with a major fault. The quartz there is very flaky and is heavily inundated with iron oxide.
Flaky Quartz

Below is an outcrop of the massive zone of foliated, flaky quartz, looking very benign, but one hammer blow reveals its secrets.

Flaky Quartz outcrop, peeking out from cover

The foliated quartz was core drilled with a backback drill 50′ deep.  The core recovery was  terrible in the flaky material, but some solid core was recovered.  Unfortunately, the supergene enrichment zone was not reached.  Below is a piece of core from 20 feet deep.

Core from 20′ deep

From 35′ deep in the hole, the acid bleaching of quartz can be seen in this piece of core shown below.
At 35′ deep, acid bleached quartz

Other quartz outcrops in the breccias on the prospect are spotted with blebs of manganese, another testament that brine was instrumental in forming the deposit.

Manganese-spotted quartz (manganese can be seen on all sides)

Similar to vents and mounds normally associated with VMS deposits, below is an almost fully intact hydrothermal silica mound heavily inundated with iron oxides on the northern end of the Prospect.  Most of this mound is highly magnetic (attracts a magnet). There is another mound of this material that can be seen to the left in the photo (to the south).  There is another large one to the right that cannot be seen. There is recent evidence that there can be as much as 5 times the volume of a mound below the sea floor for similar VMS mounds. Please note that there are three large mounds here, but as shown below and in the conclusion, there is an entire FIELD of hydrothermal silica and silicified basalt mounds exposed on the surface stretching from end-to-end of the Molly Marie Prospect.

Shown here and shown within is clear-cut geologic and archaeologic evidence on a district-wide scale that supports the Peralta Mines legend.
Silica/Jarosite mound

The bulges at the top of the mound are indicating a breccia pipe an the outcrop is shown in the photo below.
Breccia at the top of the Mound

Below is an exposure of silica beds on the south side of the north mound.  All of this material is very magnetic. The south mound has similar beds “draped” around it.
Silica beds

Below are pieces from the silica beds.  The beds break apart in flat pieces easier than if they were shale.
Broken Silica Beds

Below is the sand from a crushed piece of the silica bed material that has been rinsed to wash out the powdered hematite.  Every grain that remains is magnetic.  The below photo is of a 3/4″ diameter washer magnet covered with the sand.  When wet, most of the silica is crystal clear with finely disseminated iron oxides.
Crushed Magnetic Silica Sand.

Below is an outcrop of the beds on the north side of the north mound.
Beds on North Side of Mound

Shown below, on the southeast side of the southern Silica/iron oxide mound, there is a large area that is covered by friable exhalitive “dirty” silica beds that must have covered the entire area at one time.  This material contains much magnetite and has significant carbonates as well.
Exhalite beds

The exhalative formation shown above is more consolidated down-dip near where a significant outcrop is found under thick tuff. This is found at the base of the southern mound.  A sawn piece of it is shown below.  Abundant gossan can be seen.  It will be interesting to see how this assays.
Iron Oxide Breccia

Below is chrysocolla found at the base of the northern mound.
Chrysocolla from the base of the largest Mound

The sawn hydrothermal silica below is from one of the smaller mounds on the south side of the caldera.  The clasts of iron oxide are larger than the silica found from the large mounds.  The cloudy, delicate deposition bands can be seen.  The silica has a green tinge and in the vugs, and Actinolite? can be seen.  With a loupe, the abundant grains of magnetite are visible.
Hydrothermal Silica from a smaller mound

The silica is actually more revealing when it is broken rather than sawn.  In the piece below,  This photo is high resolution and zooming works well.
Broken Hematite Silica

If the reader has any doubt that this is hydrothermal silica, a simple test removes all doubt:  When this material is crushed and panned and the powdered hematite is washed out, the pan looks like it is full of only black sand.  But, when the grains are viewed with a loupe, they are seen as grains of clear silica coated with hematite and manganese. Below is a photo of the rock after it was crushed, after it was washed, and a close-up of the nearly 100% quartz left behind.
The crushed hydrothermal silica after being crushed, washed and magnified.

Below is what one of the smaller mounds looks like that is partially eroded.  The material in the smaller mounds is typically much softer than that found on the larger, probably due to the larger hematite fragments.   That’s Superstition Mountain in the background.  A Jerome mercury vapor detector was used in this area and the detector alarm went off frequently in the open air.
Eroded Small Mound

In the arkose breccia area, there is a great amount of broken exhalites including saccharoidal silica as in the photo below, massive silica, metalliferous mudstone, and jasper breccia.  The mound field described above is over one mile long.  Including the width of the field and the width of the breccias, the width is nearly a half a mile wide.  This indicates the footprint of the IOCG deposit.

Given an average thickness of 1000 feet, the deposit could be a BILLION tons in size.  In the photo below, fossilized microbial mat can be see to the right of the barnacle.  It is suggested that this life did not thrive around a black smoker or a white smoker, but a RED smoker, because of the large amount of hematite.

Barnacle with Microbial Mat (to the right)

Below is a piece of the friable remains of the growth from a hydrothermal vent.  This material litters the southern end of the brecciated area.
Hydrothermal vent fossil

At the top of the large north silica mound several small dikes of very olivene rich basalt can be seen.  Viewed with  a loupe, the rock is a deep dark green. This rock was likely from the bottom of the magma chamber and is highly magnetic.  It has the color of Dunite.  Note: this is toughest rock type that the author has ever broken.
Olivene-rich Basalt

On the east side of the northern mound, there is gossan found from a sulfide vein.  This vein has a strike length of about 50 feet.  Note that the full width would double if the surface material was removed.  This is evidence that the silica shown above is just a classic cap on the hydrothermal mound and below it are great amounts oxidized ore.
Gossan from a Sulfide Vein

A very large outcrop has been found that is believed to be the core of a large mound or the mineralization below it.  A photo of a piece of it is below.  It is not very exciting to look at and that must be the reason there are not too many photos of IOCG ore on the internet.  There is abundant waxy yellow apatite and tiny chalcopyrite crystals that can be seen in it with a loupe.  It is very dense and magnetic.   The outcrop is hundreds of feet long and guessing about 200 feet wide.  A couple of large chrysocolla-saturated rocks were found in this area over the past few years, and this must be the origin of the material.  The outcrop is near the the large mound shown above.

IOCG “ore”

Below is a Google Earth photo with the large mounds circled.  It is not known if something like this has ever been found before, but it is an IOCG mound field.  the cyan colored ares is where the IOCG ore outcrop is located.  It is believed that all of the larger mounds have hematite and magnetite inside and below them (and metals), very similar to a VMS deposit.
IOCG Mound Field

More geology, much history, the infrastructure of  the historic District, and the potential for great wealth left to be unearthed is shown within.

After nearly 20 years of study and fieldwork, there is now enough evidence to present the mines that used to be, and where new mines could be.

Select any of the pages in the menu to begin……..


(cover photo is a view of the Superstition Mountains from the southern end of the Molly Marie Prospect)