Gold ore often forms in hydrothermal veins related to mountain building and along fault zones. Quartz commonly forms in the bulk of the vein with smaller amounts of gold, calcite and sulphides such as pyrite. The bedrock along stream or river courses containing the quartz veins wears away through wind and water erosion leaving the vein exposed. The quartz itself also erodes allowing the "placer" gold and other heavy minerals to wash downstream and deposit in rivers and streams. Because gold is heavy, it settles out in sediment in the calm bends of the river.
Examine river bends for evidence of gold. Use a sieve to wash the sediment from the slowest part of the river, the interior of the bends. Gold is very dense and falls out of suspension where the river velocity slows.
Review the geologic map for evidence of bedrock quartz veins. The source of the gold will be upstream from the location in the river where you find the gold. Walk through the area to find outcrops of the quartz.
Collect samples of the quartz vein in several locations in the outcrop using the rock hammer. Break the quartz samples open and examine the mineral for evidence of gold ore. You may need to use a hand magnifier because gold deposits are often small.
Perform mineral identification tests on the suspected gold to identify the mineral. Some minerals, such as pyrite, look similar to gold and also form in quartz veins. Gold is very soft and you can scratch it with a copper penny or a pocketknife. Rub the gold on a white streak plate and observe the colour. Gold leaves a shiny, yellow-coloured streak. Pyrite, or "Fool's Gold," is much harder and leaves a greenish-black coloured streak. Pyrite will not show a scratch from a penny or knife. Gold is also very dense and heavy while pyrite flakes and is much lighter.
Contact a local geologist to help you identify potential quartz veins if you are not familiar with reading a geologic map or looking for outcrops. Use an unglazed tile for the streak test if you do not have a streak plate.
Modern mining techniques are typically necessary to find significant amounts of gold ore.