The Australian 1985 One Dollar coin does not have a mintmark. They were all minted at the Royal Australian Mint Canberra.
If the coin does have a mintmark it would be under the "DO" in dollar on the back of the coin.
If the coin has a Mintmark it is on the back of the coin, above the letters DO in dollar. If no mintmark the coin was minted in Philadelphia.
The last Australian Two Dollar notes were printed in 1985. The Australian Two Dollar coin was first issued in 1988. The Two Dollar notes were progressively withdrawn from circulation from 1988.
On the reverse side of the coin under the DO in DOLLAR.
If the coin has a Mintmark it is on the back of the coin, above the letters DO in dollar.
On a US silver dollar, the mintmark is in a variety of locations, on a Morgan Dollar ( 1878-1921) it is underneath the tail feathers of the eagle between the D and the O in Dollar. On a Peace Dollar (1921-1935) it is located underneath the One in "One Dollar" on the reverse on an Eisenhower Dollar (1971-1978) it is between the 3rd and 4th numbers of the date by Eisenhower's neck. If there is no mintmark, the coin was minted in Philadelphia, if there is a D mintmark, the coin was minted in Denver, if there is an O mintmark the coin was minted in New Orleans, if there is an S mintmark the coin was minted in San Fransisco and if there is a CC mintmark the coin was minted in Carson City
The Australian One Dollar coin was first issued in 1984 replacing the Australian One Dollar note which was last issued in 1982. The Australian One Dollar note was progressively removed from circulation in 1984. The Australian Two Dollar coin was first issued in 1988 replacing the Australian Two Dollar note which was last issued in 1985. The Australian Two Dollar note was progressively removed from circulation in 1988.
The first Australian Dollar coin was issued in 1984.
Australian one-dollar coin was created in 1984.
Australian two-dollar coin was created in 1988.
All 1988 Australian coins were minted at the Royal Australian Mint Canberra. Since they were all minted at the same place, there is no mintmark.
Regardless of the year the mintmark is in the same place on all Morgan silver dollars, it's on the reverse just above the letters DO in dollar. If it does not have a mintmark it was coined in Philadelphia no Morgan dollar has a "P" mintmark.