Decline – A vertical or inclined opening in a mine, driven upward from a level to connect with the level above, or to explore the ground for a limited distance above one level.

 

Deposit - An anomalous occurrence of a specific mineral or minerals within the earth’s crust.

 

Development – The work done in a mine to open up the paying ground or roof and, in particular, to form drives or haulages around blocks of ore.

 

Diamond Drill Hole – A drill hole formed by the act or process of drilling boreholes using bits inset with diamonds as the rock-cutting tool. The bits are rotated by various types and sizes of mechanisms motivated by steam, internal-combustion, hydraulic, compressed-air, or electric engines or motors.

 

Dilution – The contamination of ore with barren wall rock in stoping. The assay of the ore after mining is frequently 10% lower than when sampled in place.

 

Dip – The angle at which a bed, stratum, or vein is inclined from the horizontal, measured perpendicular to the strike and in the vertical plane.

 

Discount Factor - The discounted value of a cash flow is determined by reducing its value by the appropriate discount rate for each unit of time between the time when the cash flow is to be valued to the time of the cash-flow. Most often the discount rate is expressed as an annual rate.

 

Drill Core – A solid, cylindrical sample of rock produced by an annular drill-bit, generally rotatively driven but sometimes cut by percussive methods.

 

Drill Drive - A horizontal tunnel from which drilling for stoping operations commences.

 

Drilling Jumbo – A drill carriage or mobile scaffold on which several drills of different type are mounted. It is used in tunnels and large headings.

 

Dunite – Peridotite in which the mafic mineral is almost entirely olivine, with accessory chromite almost always present.

 

Dyke – Tabular igneous intrusion that cuts across the bedding or foliation of the country rock.

 

Drill Holes - Technically, a circular hole drilled by forces applied precussively. Loosely and commonly, the name applies to a circular hole drilled in any matter.