Case Study: Henrietta Gold Mine | Arizona, USA

Engineering Challenge

The Henrietta mine which, in the early days, was known as the Big Bug, is about one-half mile north of Big Bug Creek and one mile west of Poland siding.  The Big Bug vein, which occurs mainly in massive, fine-grained amphibolite or diorite, strikes north, dips about 70° west., and is from 2 to 6 feet wide. Its gangue consists of massive quartz with some calcite. About 60 per cent of the unoxidized ore consists of pyrite, chalcopyrite, sphalerite, and galena. Ore from the lower levels is reported to contain 3.2 percent of copper and 14 percent of iron, together with 0.2 ounces of gold and 2.7 ounces of silver per ton. With gold being the primary mineral in the mine of interest, equipment used in the mining process must be able to withstand the highly abrasive mineral.

The scalping mixer tanks for the Henrietta Mine are provided by Fluid Systems in Houston, Texas. These tanks must process a water and ore mixture with a Specific Gravity of 1.5 and an Abrasion Index of 20.  Mixers are required in the scalping tank to maintain the uniformity of the ore and water mixture, and to keep all the ore particles in suspension.  Due to the abrasive nature of the ore, the selection of a mixer was an important consideration.  DBS Representative Dean Taylor referred Fluid Systems to DBS Manufacturing for a solution to mixing in the scalping tanks for this project.

Solution 

Scalping Tanks are used to mix the crushed ore and water to maintain a uniform discharge for further processing. This mixture is very abrasive. One way wear can be reduced is by using an efficient low speed mixer. Low mixer surface speed will minimize mixer wear. The material of mixer construction is also an important consideration. The ore solution is not only abrasive, but it is also corrosive.  For this reason, stainless steel was chosen as the material of mixer construction.

The rotor design chosen for this application is the DBS hyperbolic rotor.  Hyperbolic mixers are efficient low speed mixers which are frequently used to mix large volumes in water treatment plants.  These hyperbolic mixers are most normally made from fiberglass which would not be suitable in the Scalping tank application.  The DBS hyperbolic rotor is unique in that it can be made from nearly any material that can be laser cut.  For this project Type 304 SS was chosen.  To further enhance the durability of the DBS rotor, the rotors will be coated with CeRamKote 54.  This coating has high abrasion and corrosion resistance.

Nils R. Young, PE, Director