Australia can publicly give a guarantee of sovereignty to Papua New Guinea and Indonesia wouldn't mind. Like, if Australia signs a mutual defense treaty with Papua New Guinea, well, the usual rabble-rousers will make noise but the Indonesian government as a whole would go "eh, whatever" and go on with life. A permanent stationing of Australian troops in Papua New Guinea though, with or without a guarantee of sovereignty, is going to be seen as a potential threat. Because rather than being seen as Australia trying to protect PNG, it will be seen as Australia preparing to invade West Papua instead.
Cross-checking the news article, the writer seems to be an alarmist, reading ill-intent everywhere.
Does the Indonesian Army assign soldiers to the PNG-Indonesia border? Yes, every year. It's part of the regular rotation. Malaysian-Indonesia and Timor Leste-Indonesia borders get the same treatment. Indonesia does not have a separate border patrol agency. That task falls under the armed forces' remit instead. Complicating the issue was the discovery of marijuana farms deliberately placed at the border and incidents of marijuana smuggling at the border. West Papuan rebels have also used the border as a safe zone, since the two countries do not have a "hot-pursuit"agreement. So I would not be surprised if there are soldiers patrolling the border and if there are watch posts being erected.
There is a map purporting to show that Indonesia shifted the border 12 km into PNG's side, but there is no mention of it in the article. What are we supposed to take from that? It's ridiculous to anyone who knows how the border was established. North of the Fly River bend, the border is defined as 141 E meridian. There are markers to mark the line, but the markers do not define the line. So north of the Fly River, if there is doubt over where the border is all anyone need to do is check whether the place is west or east of the 141 E meridian. (South of the Fly River the border line is slightly different.) I'm kinda surprised to hear this from a Papua New Guinean person though. Usually it's Indonesia and Malaysia who are accusing each other of moving the border markers, and that's because the Malaysian-Indonesian border isn't defined as a straight line following a certain longitude. I repeat, there is NO disputed territory between PNG and Indonesia because all one needs to determine the border is a good GPS, or in case of the Fly River bend, a good eye to see where the river is.
Next, thorium is the reason? Really? Oh boy, this is like that guy in the Philippines who insists that there is deuterium in Benham Rise and somehow managed to persuade even the Marcoses to put money into mining it because deuterium is fuel for nuclear fusion.
Look, thorium is not actually that rare. The term "rare earth" is a misnomer given because back in the 1800s the chemists had no idea how to separate them and thus only discovered a very small amount of those elements. But with modern chemistry and radiology, we can detect thorium even at concentrations not worth exploiting. And it turns out Indonesia has quite a bit of them. But whether it's worth mining is another thing. The largest proven deposit of thorium in Indonesia is in the monazite sands of Bangka Island in western Indonesia. It's the byproduct of PT Timah's tin mining and refining. PT Timah has over four hundred thousand tonnes of monazite that they don't know what to do with, since they are forbidden to release it due to its radioactivity and they can't process it because there is no thorium market. It just sits there in huge warehouses. The only demand for thorium is for research purposes, and that demand is miniscule. I'm talking global demand here. Yes, in theory thorium can be processed into nuclear fuel, but right now there are ZERO operating nuclear power plant that uses thorium. Now, Indonesia (with international help) is building a very small 10 MW reactor that in theory can use thorium, and they do plan of doing a proof-of-concept experiment with thorium in addition to the usual uranium, but yes, they do have a pilot plant capable of refining several kg of thorium and if it all works out they'll go to a 100 MW demonstration plant (all this is public data, the Indonesia submits updates of their nuclear energy plans to IAEA regularly), but to claim that this causes the Indonesian Army to go to the PNG border to seize the deposits there is ridiculous. There is a small but vocal group of Indonesians pushing for thorium-based nuclear power plants, but if you dig down into the technical documents, you will see that it's a. not going to be soon, b. envisions a dual-fuel reactor that will use uranium at first, and c. going to use the already available Bangka Island deposit. Again, public docs. There is no reason why Indonesia will need to go the the Indonesia-PNG border to get thorium. Thus I have no idea why the writer claims that thorium is the sole reason for this supposed... invasion? Theft of land? Infiltration? No idea.
Lastly, like, seriously, guys. You guys know Indonesia. Does any of you think that Indonesia can mastermind a plan to wrest a chunk of territory in order to build a vast mining operation and somehow keep it a secret? A secret so tight that no one in Indonesia and Australia know about it until a smart and observant Papua New Guinean connected all the dots together?