There is not sense in how we mine GRAMS of minerals to produce items.
We can carry dozens of backpacks with dozens of backpacks inside filled with grams of minerals.
First of all, I would change Grams to Units, so a unit of iron doesn't need to be the same grams of weight than a unit of coal or silver.
Then we could add a different weight to every Unit . For example 50u or Iron would weigh 5 kilos and represent this amount of mineral but 50u of silver could weigh 1 kilo representing much less grams of mineral and so on.
So breaking the actual grams measurement we could add a logic to the weight could be transported or when a jetpack could stop working depending on the weight.
It also would make the Rovers useful to transport big amounts of minerals.