There are many different levels of purity in the gold investment world. First and foremost, it is important to look for the amount gold, by weight, in the coin you're buying, regardless of what other less-valuable metals it has been alloyed with. This will be the most important factor come resale time.
For example, take the American Gold Eagle.
While it checks in at 91.67% purity — in addition to gold, it is 3% silver and 5.33% copper), commonly referred to as 22-karat gold, it contains the same amount of gold as the Canadian Gold Maple Leaf, which is 99.99% pure gold, more commonly referred to as 24-karat gold.
Alloying gold with more common, harder metals makes it less prone to scratches and other damage. Silver, zinc, and copper are all commonly combined with gold to make it more durable and less susceptible to visible wear. Pay attention to the total weight of pure gold per coin that you are getting. When it comes time for resale, that will be the most important factor, regardless of the other base metals it may be combined with.
Gold must have a purity higher than .900 to be considered "fine gold". Along with the American Gold Eagle, the South African Krugerrand is another gold coin that qualifies by offering 91.67% purity (the remaining 8.33% is copper).
The Krugerrand is unusual in that it has no face value. Generally, this is of little concern, as the value of the gold in 1 oz sovereign gold coins is worth many times the face value their designated face value.
If you're looking for the purest sovereign gold coin you can get, one popular choice is the Canadian Royal Mint's 1 oz Gold Maple Leaf.
At .9999 purity since 1982, it is both the height of the sovereign unadulterated gold market and a technological marvel; Gold Maple Leafs incorporate Bullion "DNA" (Digital Non-destructive Activation), an anti-counterfeiting technology that captures images of the coins and encrypts them with an algorithmic signature that is then stored in a secure database. This allows their authenticity to be verified in an instant.
Also checking in at .9999 purity is the United States Mint's 1 oz American Gold Buffalo, which features the iconic design of the 5-cent "Buffalo Nickel” (also known as “Indian Head” nickel) created by American sculptor James Earle Fraser in 1913.
If you want an official US sovereign coin (face value is $50) at peak purity, look no further.
The 1 oz Austrian Gold Philharmonic offers a symphony of design appeal and fine gold. Also 99.99% pure, Austrian Mint dates back to 1194 and pours their 800+ years of tradition and worldwide recognition into each coin.
Denominated in euros since 2002 (face value €100), the Austrian Gold Philharmonic coin has been in production since 1989.
Britain's Royal Mint joins the ranks of sovereigns checking in at .9999 purity with the 1 oz Gold Britannia. Dating back even further than its Austrian counterpart, the Royal Mint has been striking coins since 886 AD.
Featuring a design displaying Brittania, the female personification of the British Isles, each coin's trademark speckled-radial sunburst design makes them especially difficult to counterfeit.
The Perth Mint's Gold Kangaroo is another fine gold choice of .9999 purity.
Minted at a nominal $100 Australian-dollar face value, this IRA-approved coin shows Ian Rank-Broadley’s regal effigy of Her Majesty Queen Elizabeth II on the front and Australia's trademark marsupial on the back.
The Chinese Gold Panda gold coin is an outlier to the .9999 and full-troy-ounce rule of the above coins.
Weighing in at 30 grams (0.9645 troy oz.) and .999 purity, Gold Pandas are legal tender (in Chinese yuan) with a face value of ¥500.00. Whereas most sovereign gold coins retain a standard design year after year, the Gold Panda does not.
The front of the 2019 version features the Hall of Prayer for Good Harvests, which dates back to the Ming Dynasty in the 1200s, while the back depicts a mother giant panda cradling her baby against a backdrop of tall mountains along with the coin’s metric weight and purity.
The market for Gold Pandas is not as liquid as the other gold sovereigns mentioned above and its sellback value tends to reflect that. We would not recommend it as an entry-level coin.
Whichever gold coin you choose, you really can’t go wrong purchasing one full troy ounce of gold, regardless of percentage of accompanying alloys or face value. Some coins offer superior liquidity (Gold American Eagle) compared to others (Chinese Gold Panda), and their premiums reflect that market.
But overall, sovereign gold coins offer a trustworthy, reliable, globally recognized way to add to your physical gold holdings, whatever their purity.