1. Chromium and Platinum Group Metals
©2009 Dr. B. C. Paul
Acknowledgement is given to webmineral.com, geology.com, brittanica.com, webmineral.com, geology.about.com, periodictable.com, mindat.org, johnbetts-fineminerals.com, USGS Bull 1693, earthsci.org, SME Mineral Processing Handbook, icdachromium.com

2. Chromium and PGM (Platinum Group Metals)
Mantle like material intrudes into continental crust
Reacts with sulfides and metals settle out at bottom
Common way to make Nickel Sulfide Deposits
Chromium and PGMs tend to settle out in specific layers
Get a little from the Sudberry meteor impact too.

3. Settled Chromium Deposits

4. The Ocean Floor Mechanism
Ocean floor comes from mantle like material forming new crust at a spreading ocean plate boundary
Sometimes when continents collide or run into things just right a chunk of sea floor gets dragged up into a continent
Called an Ophiolite sequence
Bottom part of the ocean floor can contains pods of Chromium rich ore

5. Chromium Pods in an Ocean Floor Sequence

6. Where Chromium and PGMs are Found
Green colored areas
At plate edges are
Scooped up ocean
Floor with
Chromium pods
Black areas show
Where chromium
And PGM layers
Settled from mantle
Intrusions into
Continental crust
You can get a few placers from these primary deposits too.

7. Main Ore Mineral of Chromium is Chromite
Chromite (black) interlayered with
Sepentine (greenish)
Fresh Chromite Surface
Fe2+Cr2O4 46% Chromium
S.G – 5.1
Hardness 5.5
Color Black to Brownish black
Tends to have granular texture
Weathered
Chromite Surface

8. Platinum, Osmium, Rhodium, Ruthenium, Palladium = PGMs
Native Platinum
Native Palladium
PGMs can be native metals or substituted into other minerals

9. Sperrylite PtAs2 57% Platinum S.G. 10.5 Hardness 6-7
Metal to white and brittle

10. Podform Chromite Deposits are Smaller
22,000 tons of ore is a median – big ones may be 250,000 tons
Grade of the ore is around 46% Chromic Oxide

11. PGMs may be in the parts per billion range

12. Little Chromite Pods May be Only 143 tons
Ore grades are again around 46% Chromic oxide

13. Chromium Processing Chromite tends to be lumpy big chunks
Allows some separation in mining
Rest if needed can usually be done with gravity separation
Jigs
Heavy media separators
Tables
Lump Ore is Then Sent to Smelter Furnaces
Often melted together with iron
Some very intensive oxygen and ammonia processes may kill off residual carbon.

14. The Gravity Concentrators
Use the fact that something is heavy
Heavies have more momentum –
Shaking Tables
Heavies sink faster – Jig
Light stuff floats in a heavy fluid – Heavy Media Separator

15. PGMs – A Tough Act to Process
PGMs in a good case are associated with nickel and copper sulfides
In nasty cases some of them are trapped in gangue minerals
Try to Float out the PGMs
Then send them to the smelter

16. What Do We Use Them For
Chromium is mostly as a stainless steel alloy with some chemical and plating uses
PGMs are used mostly for catalysts for air pollution control systems, with some laboratory applications, and some jewlery

17. What is Chromium Worth?
About $0.40 to $0.60/lb (prices based on chrome content of ferro-chrome

18. What Are PGMs Worth
About $5,000 to $10,000 per lb but varies with metal
Platinum around $12,000, Palladium around $4,500
Rhodium around $12,000 to $48,000

19. Production and Reserves of Chromium

20. PGMs Production and Reserves