Complex sentence: Some gold had been some found found at the Goldstream River in 1863 and expedition did find some Leechtown but it also did mapping and collected information on mineral and agricultural potential of the Island.
Split into simpler sentences: Some gold had been found at the Goldstream River in 1863, and the expedition found some at Leechtown. The expedition also performed mapping and collected information on the mineral and agricultural potential of the island.