{{redirect, BLEG, the blogging term, List of blogging terms#B Bulk leach extractable gold, more commonly shortened to BLEG, is a

geochemical Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the ...

sampling/analysis tool used during exploration for

gold Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...

. It was developed in the early 1980s to address concerns relating to the accurately measuring fine grained gold, and dealing with problems associated with sample heterogeneity.

Analysis

A large quantity of sample (between 2 and 5 kg) is digested or leached with cold

sodium cyanide Sodium cyanide is a compound with the formula Na C N and the structure . It is a white, water-soluble solid. Cyanide has a high affinity for metals, which leads to the high toxicity of this salt. Its main application, in gold mining, also expl ...

(NaCN) solution (generally 0.1% NaCN), for one to several days (depending on the assay laboratory involved). The gold is dissolved through its formation of a cyanide complex, which is concentrated through the solvent exchange process into an organic solvent and subsequently analyzed. The use of large sample weights and solvent extraction enables low detection limits, as low as 0.1 ppb. The digest is analyzed for Au (0.01 ppb), Cu (0.01 ppm), Ag (0.5 ppb), and depending on situations, for other elements. However, gold values in BLEG are lower than total assays such as those of fire assays, as it analyzes only the fine grained gold fraction and largely ignores coarser and nuggety gold. If the need arises, a separate split of the original sample is used for pathfinder elements.

Sampling considerations

BLEG requires the collection of large samples, generally greater than 2 kg. It is necessary to collect fine sized material –

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension (chemistry), suspension with water. Silt usually ...

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...

– where the fine flakes of gold will reside. Given their shape, these fine flakes of gold do not act hydro-dynamically like heavy minerals, and will not settle in the same locations in a stream bed. Where possible, attempts should be made to sample

flash flood A flash flood is a rapid flooding of low-lying areas: washes, rivers, dry lakes and depressions. It may be caused by heavy rain associated with a severe thunderstorm, hurricane, or tropical storm, or by meltwater from ice and snow. Flash f ...

sites (where finer material concentrates) – overbank deposits.

Vs sieving

BLEG is essentially a chemical sieve, designed to focus on the fine grained gold fraction. While many exploration geologists attest to the value of BLEG, some question its value compared to analyzing a simple sieved-out fine grained fraction. BLEG has been tried and tested over 20 years, applied successfully in different climatic settings, provides robust, excellent repeatability of results and has had an important role in discovery of massive Au deposits. However, some comparisons show that fine-grained sieved samples (<75 μm) show comparable results to BLEG, making the more complex process potentially unnecessary. With the exception of BLEGs applicability over a wider range of climatic conditions, the superiority of one method over the other is, at this point, still largely determined by personal preference. Gold mining