Frequently Asked Questions

What is a porphyry copper deposit ?

Porphyry copper deposits are large relatively low grade deposits that occur in the roof zones of igneous intrusions in island arc and continental margin settings (Figure 1). The mineralisation is fracture controlled and comprises copper and copper-iron sulfides with variable concentrations of gold and/or molybdenum.


 
Figure 1: Major Copper Deposits – World Distribution

Rock and mineral types are especially important for plant design and mine planning because porphyry copper systems are typically zoned upwards and outwards from a central potassic core through sericitic, argillic and propylitic alteration assemblages (Figures 2). Hypogene copper and copper-iron sulfides are associated with potassic and sericitic alteration.

 

Figure 2: Schematic Section through a Porphyry Copper Deposit showing typical alteration zonation

Many of the early deposits exploited had well developed supergene enrichment zones immediately beneath the leached surface outcrops. These zones are higher grade than the primary mineralisation and contributed significantly to the economic viability of partially weathered deposits. Furthermore supergene minerals are amenable to heap leaching and solvent extraction technologies that allowed early production of copper metal.   Modelling of grade distribution and processing capability must take account of mineralogical and metal zonation patterns (Figure 3).


Figure 3: Typical Zonation of alteration and sulphides in a porphyry copper deposit


The bulk nature of porphyry copper deposits and the intimate association between fracturing of the host rock, pervasive alteration and mineralisation makes them amenable to open cut mining methods. Relatively small higher grade deposits may be mined by block caving.

What is copper and what is it used for ?

Copper: Used in electric cables and wires, switches, plumbing, heating, roofing and building construction, chemical and pharmaceutical machinery, alloys (brass, bronze, and a new alloy with 3% beryllium that is particularly vibration resistant), alloy castings, electroplated protective coatings and undercoats for nickel, chromium, zinc, etc., and cooking utensils. The leading producer is Chile, followed by the U.S., and Indonesia (Source: Minerals Information Institute website).

What is molybdenum and what is it used for ?

Molybdenum: The two largest uses of molybdenum are as an alloy in stainless steels and in alloy steels—these two uses consume about 60% of the molybdenum needs in the United States. Stainless steels include the strength and corrosion-resistant requirements for water distribution systems, food handling equipment, chemical processing equipment, home, hospital, and laboratory requirements. Alloy steels include the stronger and tougher steels needed to make automotive parts, construction equipment, gas transmission pipes. Other major uses as an alloy include tool steels, for things like bearings, dies, machining components, cast irons, for steel mill rolls, auto parts, crusher parts, super alloys for use in furnace parts, gas turbine parts, chemical processing equipment (Source: Minerals Information Institute website).

Molybdenum also is an important material for the chemicals and lubricant industries. Moly has uses as catalysts, paint pigments, corrosion inhibitors, smoke and flame retardants, dry lubricant (molybdenum disulfide) on space vehicles and resistant to high loads and temperatures. As a pure metal, molybdenum is used because of its high melting temperatures (4,730 F) as filament supports in light bulbs, metal-working dies and furnace parts. Major producing countries are China, Chile, and the U.S.