Rock Picks Review - ASARCO Mission Mine Tour

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ASARCO Mission Mine - Tucson, AZ

We visited the Mission Copper Mine in February of 2008 during a trip to Arizona for the Tucson Rock and Gem Show.

How To Get There

Map courtesy of ASARCO Mineral Discovery Center

The ASARCO Mission Mine and Discovery Center is located approximately 15 miles south of Tucson, AZ just off of Interstate 19 on Pima Mine Road.

ASARCO Mineral Discovery Center

Panorama of the Mission Mine Main Pit - Photos by Jeffrey Allmond

ASARCO Mineral Discovery Center
1421 W Pima Mine Road
Sahuarita, AZ 85629
Information Line - (520) 625-7513
Reservations (8 or More) (435) 864-4294
Website http://www.mineraldiscovery.com
E-mail admcinfo@asarco.com

Our Rock Picks Report

On our final day in Tucson, we decided to take a tour of the ASARCO Mission Mine. The first stop was the Mineral Discovery Center (pictured at the top of this page) which offers a short film about the production of copper at the mine and many interesting related displays including an assortment of area minerals and gems. The discovery center is free to tour and is open Tue-Sat from 9AM - 5PM. The center is also the starting point for a full tour of the mine. Tours of the mine are done 5 times per day at 9:30AM, 11AM, 12:30PM, 2PM and 3:30PM. Tour prices are:

$8.00	Adults
$6.00	Seniors (62+ yrs)
$5.00	Children (5-12 yrs)
Free	Children (0-4 yrs)

While waiting for our tour bus to arrive, we wandered around the Discovery Center and watched the informational film. To the left is an archway made from the cylinder of a ball mill that is used like a rock tumbler using 3 inch steel balls like grit to pulverize the ore. To the right is a display of native copper nodules and other copper based minerals.

The mine originally started as 4 different mines each having a series of shafts following a vein of copper but when the veins played out, the mines merged and began to change into an open pit. The ore now being dug is only 0.67% copper with trace amounts of gold, silver and other elements. The ore is predominately composed of the mineral chalcopyrite.

The tour bus loaded quickly and as we drove up to our first stop, an overlook offering a view of the entire pit, we were shown a short video on overhead monitors about the mine and its environmental concerns. The panorama photo at the top of the page was taken from the upper overlook. The main pit of the mine is approximately 2 miles from north to south, 1 and 3/4 miles from east to west and approximately 1/4 miles deep. On the way up, we paused to take a look at the main conveyors and primary crushers which crush the ore into pieces approximately 8 inches in diameter.

The overlook at the top also had several mounted binoculars so you could take a closer look at the huge trucks and machinery down in the pit which from the overlook appeared the size of ants. To the right is a photo of one of the 11 foot diameter Goodyear tires from one of the trucks to give you an idea of their size. Later on in the article I have photos of some of the machinery up close.

From the overlook, we took the bus back down to the main mill which is next to the conveyors shown above and to the right. Inside the mill, ore from the primary crushers outside, crushed to approximately 8 inch diameter is fed into a SAG (semi-autogenous) Mill which is a large barrel shaped machine that is taller than it is long and is turned by two 3000 HP electric motors. Lining the inside of the barrel are lifting plates which carry the chunks of ore mixed with water up the rotating sides of the barrel and drop them back down onto the ore at the bottom. As needed, 8 inch diameter steel balls are added to the mix when the ore begins to loose the ability to crush itself. Ore is constantly going into and out of the SAG Mill. At the output of the mill, the ore is passed over a screen and any material too large to pass through the screen is either fed back into the mill or conveyored outside to a recycle pile to be re-milled later on. Material small enough to wash through the vibrating screen at approximately 3/8 inch diameter is sent on to the 2 Ball Mills.

In the photo to the left, you can see a SAG Mill in the background left and part of the 2nd one to the far right. In the foreground is one of the 2 Ball Mills. The ball mill is similar to the SAG but is longer and driven by a single 3000 HP electric motor and is actually closer to a much larger version of the barrel type rock tumbler that many of us use. Inside the Ball Mill barrel, a slurry of ore is rotated with literally thousands of 3 inch steel balls to continue grinding the ore into a fine powder. From the Ball Mills, the fine slurry is pumped to the floatation deck where the extraction process is begun. The tanks of the flotation deck can be seen in the photo below. I this series of tanks, the slurry is mixed with milk of lime to give the mix a basic ph, pine oil to form bubbles, an alcohol to strengthen the bubbles and potassium amyl xanthate which is used as a collection agent. Air is blown into the tanks to form bubbles and the mixture is stirred to agitate it. The potassium amyl xanthate causes the chalcopyrite particles to stick to the bubbles and rise to the surface.

The chalcopyrite coated bubbles flow over the edge of the first set of tanks and are pumped outside into 2 large thickening ponds where it is dumped into the center and sprayed with water to help sink it to the bottom. A series of rotating rakes drive the sunk particles to the center of the sloping bottom of the tank to be removed and the thickened slurry is sent back inside to another bank of floatation tanks to repeat the process until the resulting mix is approximately 28% copper. The remaining slurry that settles to the bottom of the series of flotation tanks containing particles of plain waste rock is pumped into large ponds to dry and be reclaimed as usable land. Clear water is drawn off near the top of the thickening pond to be recycled. The pine oil and other chemicals are filtered out and reused. Below is a photo of one of the thickening ponds outside the main mill building.

From this point, the concentrated copper is dried and shipped to the ASARCO smelter in Hayden, Arizona to be further processed. That's an awful lot of work involved when you realize that the resulting copper concentrate is less than 1% of the original material dug from the pit.

After touring the mill building, we boarded the bus again and headed back down to the Mineral Discovery Center. As we left the bus, the driver gave each of us a sample of the ore that also contained azurite and chrysocolla which he breaks off of a large boulder brought in from another mine. If you are in Tucson and are an inquisitive sort, I highly recommend a visit to the ASARCO Mission Mine Mineral Discovery Center.

Well Done ASARCO!

Additional Photos

Close up of one of the floatation tanks showing the ore laden bubbles flowing over the edge of the tank.

The other SAG Mill (back left) and Ball Mill (front right)

A flow sheet showing the route the ore takes through the mill facility.

An old shaft mine wooden head frame used to lift ore carts out of the mine via a vertical shaft.

The two photos above show one of the bigger (but not the biggest) dump trucks used at the mine.

One of the smaller dump trucks.

One of the many cactus gardens found around the location.

An interesting purple cactus native to the area.

This is a large and very old Saguaro cactus on the property. The Saguaro grow very slowly and we were told that this particular specimen was over 400 years old.

This site was last updated 06/18/08