The gold coins were first struck to the contemporary standard of 4.4 grams and with one or more Arabic Standing figures on the obverse and an Arabic legend on the reverse. Dated coins exist from 74 AH and are named as 'Dinars'. These experimental issues were replaced in 77 AH, except in North Africa and Spain, by completely epigraphical designs very similar to the designs adopted for the silver pieces but with a shorter reverse legend and no annulets or inner circles. This type was used without appreciable change for the whole of Umayyad period, the coins being struck to a new and carefully controlled standard of 4.25 grams. This weight was reputed to be based on the average of the current Byzantine solidi, was called a mithqal, a term used earlier for 1/72 of a ratl. Evidence of the importance attached to the close control of the new Dinars is provided by the existence of glass weights, mainly from Egypt. They usually show the governor's name, sometimes the date but all marked with coin denomination.
The issues in gold from North Africa began as copies of the coins of Heraclius and his son (but with an abbreviated Kalima in Latin), the reverse 'cross on steps' losing in most cases its cross piece. Dinars, halves and thirds were struck, all to the new weight standard. Later coins are dated by the Indiction Number Method, from Indiction II (85/4) changing to the Hijra date in Roman numerals in 94 AH with Arabic phrases appearing in the field from 97 AH. In the year 100, North Africa came into line with the eastern issues although the mint is named as Ifriquiyah. The legends are shorter and the reverse has a new central inscription: "In the Name of Allah, the Merciful, the Compassionate". This was used also on the coins from Al-Andalus, and on the half and third Dinars, most of which show no mint but may well have been struck in Al-Andalus.
Full source: http://en.wikipedia.org/wiki/Gold_dinar