Well, this one was just straight mercantile opportunism on a micro level. With the opium trade re-flourishing and mobs of coolies entering Australia for work, they brought opium dealers&dens into the country. The standard dens' method was to have the opium sitting on a small ball of cotton or similar, and when you smoke it that way, most of the actual high-potency drug simply melts and runs and soaks into the cotton. So after the customers had staggered off, they had all these super-potent cotton balls remaining. Seeing the Aborigines' enormous enthusiasm for whitey's alcohol, they tried the cotton balls on them, and they loved it. Brilliant: additional market, more money. Problem: super-potent. The Aborigines would basically wander off, pass out randomly in the bush, and die. Exposure, respiratory shutdown, both, who knows. This was apparently all only out in the bush -- I haven't seen anything regarding it happening in the cities.
The whiteys eventually woke up to what was going on, had no legal traction to do anything about it, and so started hammering the city folk to sort out some laws or policing or something. I think the tipping point was when the squatters (Britain's wealthy landed gentry's unwanted kids who bought & ran the big farms) found out and started jumping up and down. There are letters on file from some of the big boys who had the direct ear by personal connection to the legislators, office-holders, etc and it seems that about then things started to happen. By this stage, the fatality estimates in the bushies' letters were around 90%.
It culminated in what I believe was the world's first ban/control of opium. eg "Aboriginals Protection and Restriction of the Sale of Opium Act 1897".
You'll note there's a sharp dislocation in publicly-presented "traditions" by Aborigines from about that time onwards -- the survivors&kids had virtually no context any more and just started making shit up. You'll see photos from the '20s of Aborigines posing in their kangaroo skin cloaks, but they're on inside out, that sort of thing.