You can invest in gold online via HDFCSec using the below codes in HDFCsec

Kotak GOLD ETF
Gold BeES
ICICI Pru Gold Exchange Traded Fund
Birla Sun Life Gold ETF
HDFC Gold Exchange Traded Fund
AXIS Gold Exchange Traded Fund
Reliance Gold Exchange Traded Fund (Div-Payt)
UTI-Gold Exchange Traded Fund (G)
SBI Gold Exchange Traded Fund (G)
DSP BR World Gold Fund - Inst
Religare Gold Exchange Traded Fund