Doubling this amount wouldnt be easy , as OP asked for on how to double this amount, it would really need investment though in able to double it but this doesnt mean that you would able to double it safely because as we all know that investment do have risk on lossing money. You could actually make some huge investments like creating a gambling site or an exchange site.
Maybe when the ZCash price drops to around $10, you can buy quite a lot of thsoe and double your money.
investing at ZCash is very risky such as gambling maybe several days ago when this coin has been lauch at exchange still profitable to save it but after seeing the current price i'm so doubt Zcash will last long at least for next several month because day by day the price dropped with pretty fast and i fear those $100.000 will be decrease and maybe OP will lost all the funds
Zcash has turned into another coin to get pumped and dumped, it started well, but the interest of the most were to make easy money, in the future im sure the market will find the real value of it, sure you can make amazing income but there are some risk. If there were a safety way to monetize a big investment it would be done already.