Gold rush period (6)
I believe the answer is:
august
'period' is the definition.
(I know that calendar month is a type of period)
'gold rush' is the wordplay.
'gold' becomes 'Au' (Au is the chemical symbol for gold).
'rush' becomes 'gust' (I have seen 'Rush of wind ' mean 'gust' so perhaps 'rush' could also mean 'gust').
'au'+'gust'='AUGUST'
(Other definitions for august that I've seen before include "days in summer" , "It follows 8" , "when students are down?" , "Distinguished" , "For Edna O'Brien, it was a 27 across month" .)