List three metals that are usually found in an uncombined state in nature and three metals that are always found in a combined state in nature.

Metals found in their natural, metallic form are known as native metals. Unlike most metals which react with other elements in the environment to form ores, native metals remain in their pure state. Gold, silver, and platinum are quintessential examples of native metals, often treasured for their lustrous appearance and rarity. These metals are highly resistant to corrosion and oxidation, which explains their natural occurrence in pure form. They can be discovered in alluvial deposits, where particles are eroded from their original rock and deposited in river beds or valleys.

Because these metals are found in a state that requires little to no refining to obtain a usable product, they have been historically significant for their immediate utility and value. Acquisition of gold nuggets or silver lodes, for instance, has driven countless explorers and prospectors throughout history to undertake perilous journeys.

In contrast to native metals, most metals are found in the earth's crust in a combined state, typically in the form of mineral ores. Iron, aluminium, and zinc are prominent examples and are never found in their pure state in nature. They react with other elements like oxygen, sulfur, or carbon to form compounds. An ore is a naturally occurring solid material from which a metal or valuable mineral can be profitably extracted. For example, bauxite is the principal ore of aluminium and hematite is one of the main sources of iron.

The process of extraction of a metal from its ore is a cornerstone of industrial metallurgy and involves several steps, including crushing, grinding, and various concentration or refining techniques. Extracting metals from their ores is an essential process in the production of metals for industrial applications.

Metallurgy is the science and technology of metals. It encompasses a broad array of practices and techniques focused on the extraction, refining, and processing of metals from ores or recycled materials. The ultimate goal is to produce metals with desired properties suitable for practical use. These processes are fundamental to human technology and economic development, as metal plays a critical role in the infrastructure and manufacturing of countless products.

The steps in metallurgy can be broadly divided into pyrometallurgy, using high temperatures to effect chemical transformations; hydrometallurgy, involving aqueous solutions to extract metals; and electrometallurgy, which utilises electrical current for the same purpose. Professionals in the field of metallurgy strive to improve both the efficiency and environmental impact of these processes.

Alluvial deposits are sediments composed of sand, gravel, minerals, or other particulate matter deposited by flowing water. These deposits can be found in river beds, floodplains, or deltas and are a significant source of native metals like gold and platinum. Metals deposited in this way are often concentrated by the natural sorting action of the water, making them more accessible for mining.

Alluvial mining involves various techniques, from panning to cradling, sluicing, and dredging, depending on the scale and nature of the operation. Such extraction methods have been used by miners historically and continue to be employed in the search for valuable minerals. Interestingly, the presence of alluvial deposits can point geologists to the location of valuable ore deposits, as they are often transported downstream from their original source.