No. The British Halfcrown has been minted from silver since the mid 17th century. Prior to that, they were sometimes minted in gold, sometimes in silver.
Yes. The British pattern gold Sovereign was only minted at the Melbourne and Sydney mints in 1897.
The were approximately 2,718,000 British 1838 gold Sovereigns minted.
British 1913 Halfcrown coins were minted in 92.55% silver only
There was no 1977 British One Pound coin minted. The first general circulation One Pound coins was minted in 1983.
Other than British gold coins such as the Half-Sovereign, Sovereign, etc., Australia has never produced "Australian" gold coins for general circulation in Australia. The Sovereign coinage minted for Britain were minted to the British pattern from gold mined in Australia and were minted at either of the Melbourne, Perth or Sydney Mints (Mintmarks M, P or S respectively).
British coins minted in 1783 include - Guinea (gold) Half-Guinea (gold) Due to Britains ongoing expenses with various wars in the late 18th and early 19th centuries, there were very few silver or copper coins minted, subsequently there were a great many counterfeit coins produced.
Since Farthings were not minted in gold, this would most likely be a Queen Victoria Coronation commemorative token or medallion. It would be worth what ever the current bullion price for gold is worth.
There were never any British Two and a Half-Sovereign coins minted.
You fail to specify what type of coin you refer to. The only gold British coin minted in 1958 was the Sovereign.
There were no British gold coins minted in 1939, and, if there were, they would have King George VI on them. There were no Queens from 1902 to 1952.
British Shillings were never minted in gold. It was only ten years earlier that were no longer minted in 50% silver. Your coin may have been plated. Modified coins have no value.
The British 1888 Sovereign minted in Melbourne (normal JEB on reverse) was minted as a "pattern" coin suggesting that there was only ever a few minted, possibly only 5 or 10. There were other variants of the same coin minted in Melbourne and elsewhere that are much more common.