Gold

Gold is a chemical element with symbol Au (from Latin: aurum) and atomic number 79. In its purest form, it is a bright, slightly reddish yellow, dense, soft, malleable and ductile metal. Chemically, gold is a transition metal and a group 11 element. It is one of the least reactive chemical elements, and is solid under standard conditions. The metal therefore occurs often in free elemental (native) form, as nuggets or grains, in rocks, in veins and in alluvial deposits. It occurs in a solid solution series with the native element silver (as electrum) and also naturally alloyed with copper and palladium. Less commonly, it occurs in minerals as gold compounds, often with tellurium (gold tellurides).

Gold's atomic number of 79 makes it one of the higher atomic number elements that occur naturally in the universe. It is thought to have been produced in supernova nucleosynthesis from the collision of two neutron stars and to have been present in the dust from which the Solar System formed. Because the Earth was molten when it was just formed, almost all of the gold present in the early Earth probably sank into the planetary core. Therefore, most of the gold that is present today in the Earth's crust and mantle is thought to have been delivered to Earth later, by asteroid impacts during the late heavy bombardment, about 4 billion years ago.

Sierra Leone

Coordinates: 8°30′N 11°30′W / 8.500°N 11.500°W / 8.500; -11.500

Sierra Leone (ⁱ/sɪˈɛərə lɪˈoʊni, -lɪˈoʊn/), officially the Republic of Sierra Leone, is a country in West Africa. It is bordered by Guinea on the north, Liberia in the south-east, and the Atlantic Ocean in the south-west. Sierra Leone has a tropical climate, with a diverse environment ranging from savannah to rainforests. Sierra Leone has a total area of 71,740 km² (27,699 sq mi) and an estimated population of 6 million (2011 United Nations estimate).Freetown is the capital, largest city, and its economic and political centre. Bo is the second largest city. The other major cities in the country with a population above 100,000 are Kenema, Makeni and Koidu Town. Sierra Leone is divided into four geographical regions: the Northern Province, Eastern Province, Southern Province and the Western Area, which are further divided into fourteen districts.

About sixteen ethnic groups inhabit Sierra Leone, each with their own language and customs. The two largest and most influential are the Temne and the Mende people. The Temne are predominantly found in the north of the country, while the Mende are predominant in the south-east. Although English is the official language spoken at schools and government administration, the Krio language is the most widely spoken language in the country and unites all the different ethnic groups in the country, especially in their trade and social interaction with each other.

Alluvium

Alluvium (from the Latin, alluvius, from alluere, "to wash against") is loose, unconsolidated (not cemented together into a solid rock) soil or sediments, which has been eroded, reshaped by water in some form, and redeposited in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel. When this loose alluvial material is deposited or cemented into a lithological unit, or lithified, it is called an alluvial deposit.

Definitions

The term "alluvium" is not typically used in situations where the formation of the sediment can clearly be attributed to another geologic process that is well described. This includes (but is not limited to): lake sediments (lacustrine), river sediments (fluvial), or glacially-derived sediments (glacial till). Sediments that are formed or deposited in a perennial stream or river are typically not referred to as alluvial.

Age

Most alluvium is geologically very young (Quaternary in age), and is often referred to as "cover" because these sediments obscure the underlying bedrock. Most sedimentary material that fills a basin ("basin fill") that is not lithified is typically lumped together as "alluvial". Alluvium of Pliocene age occurs, for example, in parts of Idaho. Alluvium of late Miocene age occurs, for example, in the valley of the San Joaquin River, California.